diff --git a/community-build/src/scala/dotty/communitybuild/projects.scala b/community-build/src/scala/dotty/communitybuild/projects.scala
index a5c482a9a339..0689b44c1012 100644
--- a/community-build/src/scala/dotty/communitybuild/projects.scala
+++ b/community-build/src/scala/dotty/communitybuild/projects.scala
@@ -315,7 +315,7 @@ object projects:
     project = "shapeless-3",
     sbtTestCommand = "testJVM; testJS",
     sbtDocCommand = forceDoc("typeable", "deriving"),
-    scalacOptions = "-source" :: "3.3" :: SbtCommunityProject.scalacOptions.filter(_ != "-Wsafe-init"), // due to -Xfatal-warnings
+    scalacOptions = "-source" :: "3.3" :: SbtCommunityProject.scalacOptions.filter(_ != "-Wsafe-init"), // due to -Werror
   )
 
   lazy val xmlInterpolator = SbtCommunityProject(
@@ -484,7 +484,7 @@ object projects:
     project = "cats",
     sbtTestCommand = "set Global/scalaJSStage := FastOptStage;rootJVM/test;rootJS/test",
     sbtPublishCommand = "rootJVM/publishLocal;rootJS/publishLocal",
-    scalacOptions = SbtCommunityProject.scalacOptions.filter(_ != "-Wsafe-init") // disable -Ysafe-init or -Wsafe-init, due to -Xfatal-warning
+    scalacOptions = SbtCommunityProject.scalacOptions.filter(_ != "-Wsafe-init") // turn off -Wsafe-init due to -Werror
   )
 
   lazy val catsMtl = SbtCommunityProject(
@@ -583,10 +583,10 @@ object projects:
     extraSbtArgs = List(s"-Dakka.build.scalaVersion=$compilerVersion"),
     sbtTestCommand = List(
       "set every targetSystemJdk := true",
-      // selectively disable -Xfatal-warnings due to deprecations
-      """set actor/Compile/scalacOptions -= "-Xfatal-warnings"""",
-      """set testkit/Compile/scalacOptions -= "-Xfatal-warnings"""",
-      """set actorTests/Compile/scalacOptions -= "-Xfatal-warnings"""",
+      // selectively turn off -Werror due to deprecations
+      """set actor/Compile/scalacOptions += "-Werror:false"""",
+      """set testkit/Compile/scalacOptions += "-Werror:false"""",
+      """set actorTests/Compile/scalacOptions += "-Werror:false"""",
       "akka-actor-tests/Test/compile",
     ).mkString("; "),
     scalacOptions = SbtCommunityProject.scalacOptions.filter(_ != "-Wsafe-init"),
diff --git a/compiler/src/dotty/tools/dotc/config/ScalaSettings.scala b/compiler/src/dotty/tools/dotc/config/ScalaSettings.scala
index 2a5db6eebf9a..9dfad99ab4b1 100644
--- a/compiler/src/dotty/tools/dotc/config/ScalaSettings.scala
+++ b/compiler/src/dotty/tools/dotc/config/ScalaSettings.scala
@@ -2,7 +2,7 @@ package dotty.tools.dotc
 package config
 
 import dotty.tools.dotc.config.PathResolver.Defaults
-import dotty.tools.dotc.config.Settings.{Setting, SettingGroup, SettingCategory, Deprecation}
+import dotty.tools.dotc.config.Settings.{Setting, SettingAlias, SettingGroup, SettingCategory, Deprecation}
 import dotty.tools.dotc.config.SourceVersion
 import dotty.tools.dotc.core.Contexts.*
 import dotty.tools.dotc.rewrites.Rewrites
@@ -40,7 +40,7 @@ abstract class ScalaSettings extends SettingGroup, AllScalaSettings:
   val forkSettings: List[Setting[?]] = settingsByCategory(ForkSetting).sortBy(_.name)
   val advancedSettings: List[Setting[?]] = settingsByCategory(AdvancedSetting).sortBy(_.name)
   val verboseSettings: List[Setting[?]] = settingsByCategory(VerboseSetting).sortBy(_.name)
-  val settingsByAliases: Map[String, Setting[?]] = allSettings.flatMap(s => s.aliases.map(_ -> s)).toMap
+  val settingsByAliases: Map[String, Setting[?]] = allSettings.flatMap(s => s.aliases.map(_.name -> s)).toMap
 
 
 trait AllScalaSettings extends CommonScalaSettings, PluginSettings, VerboseSettings, WarningSettings, XSettings, YSettings:
@@ -146,8 +146,8 @@ private sealed trait PluginSettings:
 private sealed trait VerboseSettings:
   self: SettingGroup =>
   val Vhelp: Setting[Boolean] = BooleanSetting(VerboseSetting, "V", "Print a synopsis of verbose options.")
-  val Vprint: Setting[List[String]] = PhasesSetting(VerboseSetting, "Vprint", "Print out program after", aliases = List("-Xprint"))
-  val XshowPhases: Setting[Boolean] = BooleanSetting(VerboseSetting, "Vphases", "List compiler phases.", aliases = List("-Xshow-phases"))
+  val Vprint: Setting[List[String]] = PhasesSetting(VerboseSetting, "Vprint", "Print out program after", aliases = SettingAlias("-Xprint", Deprecation()) :: Nil)
+  val XshowPhases: Setting[Boolean] = BooleanSetting(VerboseSetting, "Vphases", "List compiler phases.", aliases = SettingAlias("-Xshow-phases", Deprecation()) :: Nil)
 
   val Vprofile: Setting[Boolean] = BooleanSetting(VerboseSetting, "Vprofile", "Show metrics about sources and internal representations to estimate compile-time complexity.")
   val VprofileSortedBy = ChoiceSetting(VerboseSetting, "Vprofile-sorted-by", "key", "Show metrics about sources and internal representations sorted by given column name", List("name", "path", "lines", "tokens", "tasty", "complexity"), "")
@@ -161,7 +161,7 @@ private sealed trait WarningSettings:
   self: SettingGroup =>
 
   val Whelp: Setting[Boolean] = BooleanSetting(WarningSetting, "W", "Print a synopsis of warning options.")
-  val Werror: Setting[Boolean] = BooleanSetting(WarningSetting, "Werror", "Fail the compilation if there are any warnings.", aliases = List("-Xfatal-warnings"))
+  val Werror: Setting[Boolean] = BooleanSetting(WarningSetting, "Werror", "Fail the compilation if there are any warnings.", aliases = SettingAlias("-Xfatal-warnings", Deprecation()) :: Nil)
   val Wall: Setting[Boolean] = BooleanSetting(WarningSetting, "Wall", "Enable all warning settings.")
   private val WvalueDiscard: Setting[Boolean] = BooleanSetting(WarningSetting, "Wvalue-discard", "Warn when non-Unit expression results are unused.")
   private val WNonUnitStatement = BooleanSetting(WarningSetting, "Wnonunit-statement", "Warn when block statements are non-Unit expressions.")
diff --git a/compiler/src/dotty/tools/dotc/config/Settings.scala b/compiler/src/dotty/tools/dotc/config/Settings.scala
index 72d0b985c31b..105ebda16de1 100644
--- a/compiler/src/dotty/tools/dotc/config/Settings.scala
+++ b/compiler/src/dotty/tools/dotc/config/Settings.scala
@@ -92,6 +92,12 @@ object Settings:
     */
   type SettingDependencies = List[(Setting[?], Any)]
 
+  case class SettingAlias(name: String, deprecation: Option[Deprecation])
+  object SettingAlias:
+    given Conversion[String, SettingAlias] = SettingAlias(_, None)
+    def apply(name: String): SettingAlias = SettingAlias(name, None)
+    def apply(name: String, deprecation: Deprecation): SettingAlias = SettingAlias(name, Some(deprecation))
+
   case class Setting[T] private[Settings] (
     category: SettingCategory,
     name: String,
@@ -100,7 +106,7 @@ object Settings:
     helpArg: String = "",
     choices: Option[Seq[?]] = None,
     prefix: Option[String] = None,
-    aliases: List[String] = Nil,
+    aliases: List[SettingAlias] = Nil,
     depends: SettingDependencies = Nil,
     ignoreInvalidArgs: Boolean = false,
     preferPrevious: Boolean = false,
@@ -112,7 +118,11 @@ object Settings:
     legacyChoices: Option[Seq[?]] = None)(private[Settings] val idx: Int)(using ct: ClassTag[T]):
 
     validateSettingString(prefix.getOrElse(name))
-    aliases.foreach(validateSettingString)
+    for alias <- aliases do
+      validateSettingString(alias.name)
+      val msg = "An alias is only \"replaced by\" its primary setting; its deprecation can have only a custom message."
+      for dep <- alias.deprecation do
+        assert(!dep.replacedBy.isDefined, msg)
     assert(name.startsWith(s"-${category.prefixLetter}"), s"Setting $name does not start with category -$category")
     assert(legacyArgs || !choices.exists(_.contains("")), s"Empty string is not supported as a choice for setting $name")
     validateSettingTag(ct)
@@ -121,7 +131,7 @@ object Settings:
     // Example: -opt Main.scala would be interpreted as -opt:Main.scala, and the source file would be ignored.
     assert(!(ct == ListTag && ignoreInvalidArgs), s"Ignoring invalid args is not supported for multivalue settings: $name")
 
-    val allFullNames: List[String] = s"$name" :: s"-$name" :: aliases
+    val allFullNames: List[String] = s"$name" :: s"-$name" :: aliases.map(_.name)
 
     def valueIn(state: SettingsState): T = state.value(idx).asInstanceOf[T]
 
@@ -142,34 +152,53 @@ object Settings:
         case Some(xs)               => xs.mkString(", ")
         case None                   => ""
 
-    // Updates the state from the next arg if this setting is applicable.
-    def tryToSet(state: ArgsSummary): ArgsSummary =
-      val ArgsSummary(sstate, arg :: args, _, _) = state: @unchecked
-      def changed = sstate.wasChanged(idx)
+    /** Updates the state from the next arg if this setting is applicable. */
+    def tryToSet(state0: ArgsSummary): ArgsSummary =
+      inline def state(using ArgsSummary) = summon[ArgsSummary]
+      inline def sstate(using ArgsSummary) = state.sstate
+      inline def changed(using ArgsSummary) = sstate.wasChanged(idx)
+      val arg :: args = state0.arguments: @unchecked // there must be an arg
 
       /** Updates the value in state.
+       *
+       *  If this option is deprecated, add a warning.
+       *  If the option is `replacedBy` another option, instead of applying the value,
+       *  add the reconstructed arg to be applied subsequently.
        *
        *  @param value will be evaluated at most once for side effects
        *  @param altArg alt string to apply with alt setting if this setting is deprecated
        *  @param args remaining arguments to process
        *  @return updated argument state
        */
-      def update(value: => Any, altArg: String, args: List[String]): ArgsSummary =
-        deprecation match
-        case Some(Deprecation(msg, Some(replacedBy))) =>
-          val deprecatedMsg = s"Option $name is deprecated: $msg"
-          val altArg1 =
-            if altArg.isEmpty then List(replacedBy)
-            else List(s"$replacedBy:$altArg")
-          state.deprecated(deprecatedMsg, altArg1, args) // retry with reconstructed arg
-        case Some(Deprecation(msg, _)) =>
-          state.updated(updateIn(sstate, value), args) // allow but warn
-            .warn(s"Option $name is deprecated: $msg")
-        case None =>
-          state.updated(updateIn(sstate, value), args)
+      def update(value: => Any, altArg: String, args: List[String])(using ArgsSummary): ArgsSummary =
+        def checkDeprecatedAlias()(using ArgsSummary) =
+          val name = arg.takeWhile(_ != ':')
+          aliases.find(alt => alt.name == name && alt.deprecation.isDefined)
+          .map:
+            case SettingAlias(alt, dep) =>
+              val msg =
+                dep.collect:
+                  case dep if dep.msg.nonEmpty => dep.msg
+                .getOrElse(s"use ${this.name} instead")
+              state.warn(s"Option $alt is a deprecated alias: $msg", args)
+          .getOrElse(state)
+        def doUpdate(using ArgsSummary) =
+          deprecation match
+          case Some(Deprecation(msg, Some(replacedBy))) =>
+            val deprecatedMsg = s"Option $name is deprecated: $msg"
+            val altArg1 =
+              if altArg.isEmpty then List(replacedBy)
+              else List(s"$replacedBy:$altArg")
+            state.deprecated(deprecatedMsg, altArg1, args) // retry with reconstructed arg
+          case Some(Deprecation(msg, _)) =>
+            state.updated(updateIn(sstate, value), args) // allow but warn
+              .warn(s"Option $name is deprecated: $msg")
+          case None =>
+            state.updated(updateIn(sstate, value), args)
+        doUpdate(using checkDeprecatedAlias())
       end update
 
-      def setBoolean(argValue: String, args: List[String]) =
+      def setBoolean(argValue: String, args: List[String])(using ArgsSummary) =
         def checkAndSet(v: Boolean) =
           val dubious = changed && v != valueIn(sstate).asInstanceOf[Boolean]
           if dubious then
@@ -183,7 +212,7 @@ object Settings:
         else if argValue.equalsIgnoreCase("false") then checkAndSet(false)
         else state.fail(s"$argValue is not a valid choice for Boolean flag $name", args)
 
-      def setString(argValue: String, args: List[String]) =
+      def setString(argValue: String, args: List[String])(using ArgsSummary) =
         choices match
         case Some(choices) if !choices.contains(argValue) =>
           state.fail(s"$argValue is not a valid choice for $name", args)
@@ -193,7 +222,7 @@ object Settings:
           else
             update(argValue, argValue, args)
 
-      def setInt(argValue: String, args: List[String]) =
+      def setInt(argValue: String, args: List[String])(using ArgsSummary) =
         argValue.toIntOption.map: intValue =>
           choices match
           case Some(r: Range) if intValue < r.head || r.last < intValue =>
@@ -207,7 +236,7 @@ object Settings:
         .getOrElse:
           state.fail(s"$argValue is not an integer argument for $name", args)
 
-      def setOutput(arg: String, args: List[String]) =
+      def setOutput(arg: String, args: List[String])(using ArgsSummary) =
         val path = Directory(arg)
         val isJar = path.ext.isJar
         if (!isJar && !path.isDirectory) then
@@ -221,7 +250,7 @@ object Settings:
 
       // argRest is the remainder of -foo:bar if any. This setting will receive a value from argRest or args.head.
       // useArg means use argRest even if empty.
-      def doSet(argRest: String, useArg: Boolean): ArgsSummary =
+      def doSet(argRest: String, useArg: Boolean)(using ArgsSummary): ArgsSummary =
         def missingArg =
           val msg = s"missing argument for option $name"
           if ignoreInvalidArgs then state.warn(s"$msg, the tag was ignored", args) else state.fail(msg, args)
@@ -248,12 +277,12 @@ object Settings:
           doSet(arg1, args1)
       end doSet
 
-      def setVersion(arg: String, args: List[String]) =
+      def setVersion(arg: String, args: List[String])(using ArgsSummary) =
         ScalaVersion.parse(arg) match
         case Success(v) => update(v, arg, args)
         case Failure(e) => state.fail(e.getMessage, args)
 
-      def setMultivalue(arg: String, args: List[String]) =
+      def setMultivalue(arg: String, args: List[String])(using ArgsSummary) =
         val split = arg.split(",").toList
         def setOrUpdate(actual: List[String]) =
           val updated =
@@ -286,21 +315,25 @@ object Settings:
         allFullNames.exists(_ == name) || prefix.exists(arg.startsWith)
 
       if matches then
+        given ArgsSummary = state0
         deprecation match
         case Some(Deprecation(msg, _)) if ignoreInvalidArgs => // a special case for Xlint
           state.warn(s"Option $name is deprecated: $msg", args)
         case _ =>
           prefix match
           case Some(prefix) =>
-            // todo an error if empty suffix
-            doSet(arg.drop(prefix.length), useArg = true)
+            val value = arg.drop(prefix.length)
+            if value.isEmpty then
+              state.warn(s"Option $name requires a suffix: $arg", args)
+            else
+              doSet(value, useArg = true)
           case none =>
             val split = arg.split(":", 2)
             if split.length == 1 then
               doSet("", useArg = false)
             else
               doSet(split(1), useArg = true)
-      else state
+      else state0
 
     end tryToSet
   end Setting
@@ -342,6 +375,7 @@ object Settings:
   )
 
   object Deprecation:
+    def apply(): Deprecation = Deprecation(msg = "", replacedBy = None)
     def renamed(replacement: String) = Some(Deprecation(s"Use $replacement instead.", Some(replacement)))
     def removed(removedVersion: Option[String] = None) =
       val msg = removedVersion.map(" in " + _).getOrElse(".")
@@ -418,37 +452,37 @@ object Settings:
       assert(!name.startsWith("-"), s"Setting $name cannot start with -")
       "-" + name
 
-    def BooleanSetting(category: SettingCategory, name: String, descr: String, initialValue: Boolean = false, aliases: List[String] = Nil, preferPrevious: Boolean = false, deprecation: Option[Deprecation] = None, ignoreInvalidArgs: Boolean = false): Setting[Boolean] =
+    def BooleanSetting(category: SettingCategory, name: String, descr: String, initialValue: Boolean = false, aliases: List[SettingAlias] = Nil, preferPrevious: Boolean = false, deprecation: Option[Deprecation] = None, ignoreInvalidArgs: Boolean = false): Setting[Boolean] =
       publish(Setting(category, prependName(name), descr, initialValue, aliases = aliases, preferPrevious = preferPrevious, deprecation = deprecation, ignoreInvalidArgs = ignoreInvalidArgs))
 
-    def StringSetting(category: SettingCategory, name: String, helpArg: String, descr: String, default: String, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None, depends: SettingDependencies = Nil): Setting[String] =
+    def StringSetting(category: SettingCategory, name: String, helpArg: String, descr: String, default: String, aliases: List[SettingAlias] = Nil, deprecation: Option[Deprecation] = None, depends: SettingDependencies = Nil): Setting[String] =
       publish(Setting(category, prependName(name), descr, default, helpArg, aliases = aliases, deprecation = deprecation, depends = depends))
 
-    def ChoiceSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[String], default: String, aliases: List[String] = Nil, legacyArgs: Boolean = false, deprecation: Option[Deprecation] = None): Setting[String] =
+    def ChoiceSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[String], default: String, aliases: List[SettingAlias] = Nil, legacyArgs: Boolean = false, deprecation: Option[Deprecation] = None): Setting[String] =
       publish(Setting(category, prependName(name), descr, default, helpArg, Some(choices), aliases = aliases, legacyArgs = legacyArgs, deprecation = deprecation))
 
-    def MultiChoiceSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[String], default: List[String] = Nil, legacyChoices: List[String] = Nil, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None): Setting[List[String]] =
+    def MultiChoiceSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[String], default: List[String] = Nil, legacyChoices: List[String] = Nil, aliases: List[SettingAlias] = Nil, deprecation: Option[Deprecation] = None): Setting[List[String]] =
       publish(Setting(category, prependName(name), descr, default, helpArg, Some(choices), legacyChoices = Some(legacyChoices), aliases = aliases, deprecation = deprecation))
 
-    def MultiChoiceHelpSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[ChoiceWithHelp[String]], default: List[ChoiceWithHelp[String]], legacyChoices: List[String] = Nil, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None): Setting[List[ChoiceWithHelp[String]]] =
+    def MultiChoiceHelpSetting(category: SettingCategory, name: String, helpArg: String, descr: String, choices: List[ChoiceWithHelp[String]], default: List[ChoiceWithHelp[String]], legacyChoices: List[String] = Nil, aliases: List[SettingAlias] = Nil, deprecation: Option[Deprecation] = None): Setting[List[ChoiceWithHelp[String]]] =
       publish(Setting(category, prependName(name), descr, default, helpArg, Some(choices), legacyChoices = Some(legacyChoices), aliases = aliases, deprecation = deprecation))
 
-    def IntSetting(category: SettingCategory, name: String, descr: String, default: Int, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None): Setting[Int] =
+    def IntSetting(category: SettingCategory, name: String, descr: String, default: Int, aliases: List[SettingAlias] = Nil, deprecation: Option[Deprecation] = None): Setting[Int] =
       publish(Setting(category, prependName(name), descr, default, aliases = aliases, deprecation = deprecation))
 
     def IntChoiceSetting(category: SettingCategory, name: String, descr: String, choices: Seq[Int], default: Int, deprecation: Option[Deprecation] = None): Setting[Int] =
       publish(Setting(category, prependName(name), descr, default, choices = Some(choices), deprecation = deprecation))
 
-    def MultiStringSetting(category: SettingCategory, name: String, helpArg: String, descr: String, default: List[String] = Nil, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None): Setting[List[String]] =
+    def MultiStringSetting(category: SettingCategory, name: String, helpArg: String, descr: String, default: List[String] = Nil, aliases: List[SettingAlias] = Nil, deprecation: Option[Deprecation] = None): Setting[List[String]] =
       publish(Setting(category, prependName(name), descr, default, helpArg, aliases = aliases, deprecation = deprecation))
 
-    def OutputSetting(category: SettingCategory, name: String, helpArg: String, descr: String, default: AbstractFile, aliases: List[String] = Nil, preferPrevious: Boolean = false, deprecation: Option[Deprecation] = None): Setting[AbstractFile] =
+    def OutputSetting(category: SettingCategory, name: String, helpArg: String, descr: String, default: AbstractFile, aliases: List[SettingAlias] = Nil, preferPrevious: Boolean = false, deprecation: Option[Deprecation] = None): Setting[AbstractFile] =
       publish(Setting(category, prependName(name), descr, default, helpArg, aliases = aliases, preferPrevious = preferPrevious, deprecation = deprecation))
 
-    def PathSetting(category: SettingCategory, name: String, descr: String, default: String, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None): Setting[String] =
+    def PathSetting(category: SettingCategory, name: String, descr: String, default: String, aliases: List[SettingAlias] = Nil, deprecation: Option[Deprecation] = None): Setting[String] =
       publish(Setting(category, prependName(name), descr, default, aliases = aliases, deprecation = deprecation))
 
-    def PhasesSetting(category: SettingCategory, name: String, descr: String, default: String = "", aliases: List[String] = Nil, deprecation: Option[Deprecation] = None, depends: SettingDependencies = Nil): Setting[List[String]] =
+    def PhasesSetting(category: SettingCategory, name: String, descr: String, default: String = "", aliases: List[SettingAlias] = Nil, deprecation: Option[Deprecation] = None, depends: SettingDependencies = Nil): Setting[List[String]] =
       publish(Setting(category, prependName(name), descr, if (default.isEmpty) Nil else List(default), aliases = aliases, deprecation = deprecation, depends = depends))
 
     def PrefixSetting(category: SettingCategory, name0: String, descr: String, deprecation: Option[Deprecation] = None): Setting[List[String]] =
@@ -459,7 +493,7 @@ object Settings:
     def VersionSetting(category: SettingCategory, name: String, descr: String, default: ScalaVersion = NoScalaVersion, legacyArgs: Boolean = false, deprecation: Option[Deprecation] = None): Setting[ScalaVersion] =
       publish(Setting(category, prependName(name), descr, default, legacyArgs = legacyArgs, deprecation = deprecation))
 
-    def OptionSetting[T: ClassTag](category: SettingCategory, name: String, descr: String, aliases: List[String] = Nil, deprecation: Option[Deprecation] = None): Setting[Option[T]] =
+    def OptionSetting[T: ClassTag](category: SettingCategory, name: String, descr: String, aliases: List[SettingAlias] = Nil, deprecation: Option[Deprecation] = None): Setting[Option[T]] =
       publish(Setting(category, prependName(name), descr, None, propertyClass = Some(summon[ClassTag[T]].runtimeClass), aliases = aliases, deprecation = deprecation))
 
   end SettingGroup
diff --git a/compiler/src/dotty/tools/dotc/reporting/Reporter.scala b/compiler/src/dotty/tools/dotc/reporting/Reporter.scala
index 9465b1c6738e..d52d92dcb825 100644
--- a/compiler/src/dotty/tools/dotc/reporting/Reporter.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/Reporter.scala
@@ -232,7 +232,7 @@ abstract class Reporter extends interfaces.ReporterResult {
 
   def finalizeReporting()(using Context) =
     if (hasWarnings && ctx.settings.Werror.value)
-      report(new Error("No warnings can be incurred under -Werror (or -Xfatal-warnings)", NoSourcePosition))
+      report(new Error("No warnings can be incurred under -Werror", NoSourcePosition))
 
   /** Summary of warnings and errors */
   def summary: String =
diff --git a/compiler/test/dotty/tools/dotc/SettingsTests.scala b/compiler/test/dotty/tools/dotc/SettingsTests.scala
index 37d278b43a0a..8ec63f90c1a2 100644
--- a/compiler/test/dotty/tools/dotc/SettingsTests.scala
+++ b/compiler/test/dotty/tools/dotc/SettingsTests.scala
@@ -407,6 +407,73 @@ class SettingsTests:
       testValues(summary = summaryColon)
       testValues(summary = summaryWhitespace)
 
+  @Test def `prefix option requires nonempty suffix`: Unit =
+    object Settings extends SettingGroup:
+      val jvmargs  = PrefixSetting(RootSetting, "J<flag>", "Pass -J<flag> directly to the runtime system.")
+    import Settings.*
+    val args = List("-J")
+    val summary = processArguments(args, processAll = true)
+    withProcessedArgs(summary):
+      assertTrue("Nothing to see here", summary.errors.isEmpty)
+      assertEquals(1, summary.warnings.length)
+      assertTrue("Prefix option warns", summary.warnings.head.contains("requires a suffix"))
+      assertTrue("Prefix option is empty", jvmargs.value.isEmpty)
+
+  @Test def `alias deprecation is honored`: Unit =
+    object Settings extends SettingGroup:
+      val flag = BooleanSetting(RootSetting, "yas", "Yes, do it!",
+        aliases = SettingAlias("-meh", Deprecation("that was a dumb flag name")) :: Nil,
+      )
+    import Settings.*
+    val args = List("-meh")
+    val summary = processArguments(args, processAll = true)
+    withProcessedArgs(summary):
+      assertTrue("Nothing to see here", summary.errors.isEmpty)
+      assertEquals(1, summary.warnings.length)
+      assertEquals("Option -meh is a deprecated alias: that was a dumb flag name", summary.warnings.head)
+      assertTrue("flag was set anyway", flag.value)
+
+  @Test def `alias deprecation is honored when primary option is deprecated`: Unit =
+    object Settings extends SettingGroup:
+      val flag = BooleanSetting(RootSetting, "yas", "Yes, do it!",
+        aliases = SettingAlias("-meh", Deprecation("that was a dumb flag name")) :: Nil,
+        deprecation = Deprecation.removed(),
+      )
+    import Settings.*
+    val args = List("-meh")
+    val summary = processArguments(args, processAll = true)
+    withProcessedArgs(summary):
+      assertTrue("Nothing to see here", summary.errors.isEmpty)
+      assertEquals(2, summary.warnings.length)
+      assertEquals("Option -meh is a deprecated alias: that was a dumb flag name", summary.warnings.head)
+      assertEquals("Option -yas is deprecated: Scheduled for removal.", summary.warnings(1))
+      assertTrue("flag was set anyway", flag.value)
+
+  @Test def `alias deprecation respects primary rename`: Unit =
+    object Settings extends SettingGroup:
+      val flag = BooleanSetting(RootSetting, "yas", "Yes, do it!",
+        aliases = SettingAlias("-meh", Deprecation("that was a dumb flag name")) :: Nil,
+        deprecation = Deprecation.renamed("anything!"),
+      )
+    import Settings.*
+    val args = List("-meh")
+    val summary = processArguments(args, processAll = true)
+    withProcessedArgs(summary):
+      assertTrue("Nothing to see here", summary.errors.isEmpty)
+      assertEquals(2, summary.warnings.length)
+      assertEquals("Option -meh is a deprecated alias: that was a dumb flag name", summary.warnings.head)
+      assertEquals("Option -yas is deprecated: Use anything! instead.", summary.warnings(1))
+      assertFalse("flag was set anyway", flag.value)
+
+  @Test def `alias deprecation can't be replaced by anything`: Unit =
+    object Settings extends SettingGroup:
+      val flag = BooleanSetting(RootSetting, "yas", "Yes, do it!",
+        aliases = SettingAlias("-meh", Deprecation.renamed("anything at all!")) :: Nil,
+      )
+    import Settings.*
+    assertThrows[AssertionError](_.getMessage.contains("replaced by")):
+      flag
+
   // use the supplied summary for evaluating settings
   private def withProcessedArgs(summary: ArgsSummary)(f: SettingsState ?=> Unit) = f(using summary.sstate)
 
diff --git a/compiler/test/dotty/tools/dotc/config/ScalaSettingsTests.scala b/compiler/test/dotty/tools/dotc/config/ScalaSettingsTests.scala
index deb4fe9e57a3..c36e15a0eb36 100644
--- a/compiler/test/dotty/tools/dotc/config/ScalaSettingsTests.scala
+++ b/compiler/test/dotty/tools/dotc/config/ScalaSettingsTests.scala
@@ -160,34 +160,37 @@ class ScalaSettingsTests:
     assert(conf.errors.isEmpty)
 
   @nowarn("cat=deprecation")
-  @Test def `Deprecated options aliases are correctly mapped to their replacements`: Unit =
-    def createTestCase(oldSetting: Setting[?], newSetting: Setting[?], value: String = "") =
-      oldSetting.aliases.map: alias =>
-        s"$alias$value" -> newSetting
-
+  @Test def `Aliases of deprecated options are correctly mapped to their replacements`: Unit =
     val settings = ScalaSettings
-    List(
-      createTestCase(settings.YtermConflict         , settings.XtermConflict, ":package"),
-      createTestCase(settings.YnoGenericSig         , settings.XnoGenericSig),
-      createTestCase(settings.Ydumpclasses          , settings.Xdumpclasses,":./"),
-      createTestCase(settings.YjarCompressionLevel  , settings.XjarCompressionLevel,":0"),
-      createTestCase(settings.YkindProjector        , settings.XkindProjector, ":underscores"),
-      createTestCase(settings.YdropComments         , settings.XdropComments),
-      createTestCase(settings.YcookComments         , settings.XcookComments),
-      createTestCase(settings.YreadComments         , settings.XreadComments),
-      createTestCase(settings.YnoDecodeStacktraces  , settings.XnoEnrichErrorMessages),
-      createTestCase(settings.YnoEnrichErrorMessages, settings.XnoEnrichErrorMessages),
-      createTestCase(settings.YdebugMacros          , settings.XdebugMacros),
+    val tests = List(
+      settings.YtermConflict          -> settings.XtermConflict :* "package",
+      settings.YnoGenericSig          -> settings.XnoGenericSig,
+      settings.Ydumpclasses           -> settings.Xdumpclasses :* "./",
+      settings.YjarCompressionLevel   -> settings.XjarCompressionLevel :* "0",
+      settings.YkindProjector         -> settings.XkindProjector :* "underscores",
+      settings.YdropComments          -> settings.XdropComments,
+      settings.YcookComments          -> settings.XcookComments,
+      settings.YreadComments          -> settings.XreadComments,
+      settings.YnoDecodeStacktraces   -> settings.XnoEnrichErrorMessages,
+      settings.YnoEnrichErrorMessages -> settings.XnoEnrichErrorMessages,
+      settings.YdebugMacros           -> settings.XdebugMacros,
+      settings.YcheckInit             -> settings.WsafeInit,
       // createTestCase(settings.YjavaTasty            , settings.XjavaTasty),
       // createTestCase(settings.YearlyTastyOutput     , settings.XearlyTastyOutput, ":./"),
       // createTestCase(settings.YallowOutlineFromTasty, settings.XallowOutlineFromTasty),
-      createTestCase(settings.YcheckInit            , settings.WsafeInit),
       // createTestCase(settings.Xlint                 , settings.Wshadow, ":all"), // this setting is not going to be mapped to replacement. Read more in the commit message
-    ).flatten.map: (deprecatedArgument, newSetting) =>
-      val args = List(deprecatedArgument)
-      val argSummary = ArgsSummary(settings.defaultState, args, errors = Nil, warnings = Nil)
+    )
+    for
+      test <- tests
+      (old: Setting[?], fwd: Setting[?]) = test.take(2): @unchecked
+      SettingAlias(alias, _) <- old.aliases
+    do
+      assert(old.deprecation.isDefined)
+      val argString = if test.size > 2 then s"$alias:${test(2)}" else alias
+      val argSummary = ArgsSummary(settings.defaultState, arguments = argString :: Nil, errors = Nil, warnings = Nil)
       val conf = settings.processArguments(argSummary, processAll = true, skipped = Nil)
-      assert(!newSetting.isDefaultIn(conf.sstate), s"Setting alias $deprecatedArgument was not forwarded to ${newSetting.name}")
+      def problem = s"Setting alias $argString was not forwarded to ${fwd.name}"
+      assert(!fwd.isDefaultIn(conf.sstate), problem)
 
   @Test def `i18367 rightmost WConf flags take precedence over flags to the left`: Unit =
     import reporting.{Action, Diagnostic}
@@ -306,4 +309,12 @@ class ScalaSettingsTests:
       assertEquals(0, result.warnings.length)
       assertEquals(1, result.errors.length)
 
+  @Test def `deprecated aliases warn`: Unit =
+    val settings = ScalaSettings
+    val args = "-Xfatal-warnings" :: "-Xprint" :: "typer" :: Nil
+    val result = settings.processArguments(args, processAll = true)
+    assertEquals(2, result.warnings.length)
+    assertEquals("Option -Xfatal-warnings is a deprecated alias: use -Werror instead", result.warnings.head)
+    assertEquals(0, result.errors.length)
+
 end ScalaSettingsTests
diff --git a/repl/test-resources/repl/rewrite-messages b/repl/test-resources/repl/rewrite-messages
index d7bcbe5d3a90..2f78486782c6 100644
--- a/repl/test-resources/repl/rewrite-messages
+++ b/repl/test-resources/repl/rewrite-messages
@@ -4,7 +4,7 @@ scala> import scala.util._
 1 | import scala.util._
   |                   ^
   |         `_` is no longer supported for a wildcard import; use `*` instead
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
 1 warning found
 1 error found
 scala> extension (x: Int) def foo(y: Int) = x + y
@@ -15,6 +15,6 @@ scala> 2 foo 4
   |   ^^^
   |Alphanumeric method foo is not declared infix; it should not be used as infix operator.
   |Instead, use method syntax .foo(...) or backticked identifier `foo`.
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
 1 warning found
-1 error found
\ No newline at end of file
+1 error found
diff --git a/sbt-test/source-dependencies/changedTypeOfChildOfSealed/incOptions.properties b/sbt-test/source-dependencies/changedTypeOfChildOfSealed/incOptions.properties
index fad0545c8f66..c2b3d1a2b4a8 100644
--- a/sbt-test/source-dependencies/changedTypeOfChildOfSealed/incOptions.properties
+++ b/sbt-test/source-dependencies/changedTypeOfChildOfSealed/incOptions.properties
@@ -1 +1 @@
-scalac.options = -Xfatal-warnings
\ No newline at end of file
+scalac.options = -Werror
diff --git a/sbt-test/source-dependencies/sealed-extends-sealed/project/DottyInjectedPlugin.scala b/sbt-test/source-dependencies/sealed-extends-sealed/project/DottyInjectedPlugin.scala
index fc8fd26fc29e..88e5199c45d5 100644
--- a/sbt-test/source-dependencies/sealed-extends-sealed/project/DottyInjectedPlugin.scala
+++ b/sbt-test/source-dependencies/sealed-extends-sealed/project/DottyInjectedPlugin.scala
@@ -7,6 +7,6 @@ object DottyInjectedPlugin extends AutoPlugin {
 
   override val projectSettings = Seq(
     scalaVersion := sys.props("plugin.scalaVersion"),
-    scalacOptions ++= Seq("-source:3.0-migration", "-Xfatal-warnings")
+    scalacOptions ++= Seq("-source:3.0-migration", "-Werror")
   )
 }
diff --git a/sbt-test/source-dependencies/sealed/test b/sbt-test/source-dependencies/sealed/test
index 69c8ebe98a74..0ee9b910a31f 100644
--- a/sbt-test/source-dependencies/sealed/test
+++ b/sbt-test/source-dependencies/sealed/test
@@ -1,4 +1,4 @@
-> 'set scalacOptions += "-Xfatal-warnings"'
+> 'set scalacOptions += "-Werror"'
 
 > compile
 
@@ -8,4 +8,4 @@ $ copy-file changes/A.scala A.scala
 # D.scala needs recompiling because the pattern match in D
 # is no longer exhaustive, which should be a warning
 # there is no way to make warnings errors, so this has to be manually checked
--> compile
\ No newline at end of file
+-> compile
diff --git a/sbt-test/tasty-compat/add-overload/build.sbt b/sbt-test/tasty-compat/add-overload/build.sbt
index 52a04f07148e..4c69acb7a34f 100644
--- a/sbt-test/tasty-compat/add-overload/build.sbt
+++ b/sbt-test/tasty-compat/add-overload/build.sbt
@@ -16,7 +16,7 @@ lazy val `a-changes` = project.in(file("a-changes"))
 
 lazy val c = project.in(file("."))
   .settings(
-    scalacOptions ++= Seq("-from-tasty", "-Ycheck:readTasty", "-Xfatal-warnings"),
+    scalacOptions ++= Seq("-from-tasty", "-Ycheck:readTasty", "-Werror"),
     Compile / sources := Seq(new java.io.File("c-input/B.tasty")),
     Compile / unmanagedClasspath += (ThisBuild / baseDirectory).value / "c-input",
     Compile / classDirectory := (ThisBuild / baseDirectory).value / "c-output"
diff --git a/sbt-test/tasty-compat/add-param-unroll/build.sbt b/sbt-test/tasty-compat/add-param-unroll/build.sbt
index 24bf7f140cd1..e857fd5e1fac 100644
--- a/sbt-test/tasty-compat/add-param-unroll/build.sbt
+++ b/sbt-test/tasty-compat/add-param-unroll/build.sbt
@@ -29,7 +29,7 @@ lazy val c = project.in(file("c"))
   .settings(commonSettings)
   .settings(printSettings)
   .settings(
-    // scalacOptions ++= Seq("-from-tasty", "-Ycheck:readTasty", "-Xfatal-warnings", "-Vprint:readTasty", "-Xprint-types"),
+    // scalacOptions ++= Seq("-from-tasty", "-Ycheck:readTasty", "-Werror", "-Vprint:readTasty", "-Xprint-types"),
     // Compile / sources := Seq(new java.io.File("c-input/B.tasty")),
     Compile / unmanagedClasspath += (ThisBuild / baseDirectory).value / "c-input",
     Compile / classDirectory := (ThisBuild / baseDirectory).value / "c-output"
diff --git a/tests/disabled/macro/pos/t8013/inpervolated_2.scala b/tests/disabled/macro/pos/t8013/inpervolated_2.scala
index cbe5139cef5a..d2cacd86e1ea 100644
--- a/tests/disabled/macro/pos/t8013/inpervolated_2.scala
+++ b/tests/disabled/macro/pos/t8013/inpervolated_2.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Xlint
+//> using options -Werror -Xlint
 package t8013
 
 // unsuspecting user of perverse macro
diff --git a/tests/disabled/partest/neg/t5663-badwarneq.scala b/tests/disabled/partest/neg/t5663-badwarneq.scala
index 1cc554264ce4..8e32d55b9900 100644
--- a/tests/disabled/partest/neg/t5663-badwarneq.scala
+++ b/tests/disabled/partest/neg/t5663-badwarneq.scala
@@ -24,7 +24,7 @@ final case class ValueClass3(val value: Int) extends AnyVal
 
 /* It's not possible to run partest without -deprecation.
  * Since detecting the warnings requires a neg test with
- * -Xfatal-warnings, and deprecation terminates the compile,
+ * -Werror and deprecation terminates the compile,
  * we'll just comment out the nasty part.  The point was
  * just to show there's nothing special about a trait
  * that extends a case class, which is only permitted
diff --git a/tests/explicit-nulls/neg-patmat/match-pat.scala b/tests/explicit-nulls/neg-patmat/match-pat.scala
index 1b93267d8fe3..2357a585635e 100644
--- a/tests/explicit-nulls/neg-patmat/match-pat.scala
+++ b/tests/explicit-nulls/neg-patmat/match-pat.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class Foo {
 
diff --git a/tests/explicit-nulls/pos/match-pat.scala b/tests/explicit-nulls/pos/match-pat.scala
index 33013d1865fd..2b0b5e64dbbf 100644
--- a/tests/explicit-nulls/pos/match-pat.scala
+++ b/tests/explicit-nulls/pos/match-pat.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 // Ensure we don't get "the type test for argType cannot be checked at runtime" warning
 
diff --git a/tests/explicit-nulls/pos/unsafe-match-null-pat.scala b/tests/explicit-nulls/pos/unsafe-match-null-pat.scala
index ff31642a4027..4c46959e78b1 100644
--- a/tests/explicit-nulls/pos/unsafe-match-null-pat.scala
+++ b/tests/explicit-nulls/pos/unsafe-match-null-pat.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.language.unsafeNulls
 
diff --git a/tests/neg-custom-args/captures/capt-wf.scala b/tests/neg-custom-args/captures/capt-wf.scala
index 7521a0e26472..1f6bf5b16ac6 100644
--- a/tests/neg-custom-args/captures/capt-wf.scala
+++ b/tests/neg-custom-args/captures/capt-wf.scala
@@ -1,4 +1,4 @@
-//> using options -language:experimental.captureChecking -Xfatal-warnings
+//> using options -language:experimental.captureChecking -Werror
 import caps.cap
 class C
 type Cap = C^
@@ -35,4 +35,4 @@ def test(c: Cap, other: String): Unit =
   val y3: String^{ev} = ??? // error cs is empty
 
   ()
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg-custom-args/sourcepath2/hi/A.check b/tests/neg-custom-args/sourcepath2/hi/A.check
index 6267edaac603..d44b67b8cd53 100644
--- a/tests/neg-custom-args/sourcepath2/hi/A.check
+++ b/tests/neg-custom-args/sourcepath2/hi/A.check
@@ -4,4 +4,4 @@
   |      class Hello is in the wrong directory.
   |      It was declared to be in package <empty>
   |      But it is found in directory     hi
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg-custom-args/wildcards.scala b/tests/neg-custom-args/wildcards.scala
index c734e2d046b5..049f998324ee 100644
--- a/tests/neg-custom-args/wildcards.scala
+++ b/tests/neg-custom-args/wildcards.scala
@@ -1,6 +1,6 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 object Test {
   val xs: List[_] = List(1, 2, 3)  // error
   val ys: Map[_ <: AnyRef, _ >: Null] = Map() // error // error
-}
\ No newline at end of file
+}
diff --git a/tests/neg-deep-subtype/i17435.scala b/tests/neg-deep-subtype/i17435.scala
index aec165a18f56..9f77fc673168 100644
--- a/tests/neg-deep-subtype/i17435.scala
+++ b/tests/neg-deep-subtype/i17435.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.collection.mutable
 
diff --git a/tests/neg-deep-subtype/i5495.scala b/tests/neg-deep-subtype/i5495.scala
index 7d50c9761c30..db2610e10f6d 100644
--- a/tests/neg-deep-subtype/i5495.scala
+++ b/tests/neg-deep-subtype/i5495.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class A
 class B
diff --git a/tests/neg-deep-subtype/i5826b.scala b/tests/neg-deep-subtype/i5826b.scala
index a3c3382bbc51..31d505c1b844 100644
--- a/tests/neg-deep-subtype/i5826b.scala
+++ b/tests/neg-deep-subtype/i5826b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class Foo {
   def test1[A]: List[Int] | A => Int = {
diff --git a/tests/neg-deep-subtype/patmat-applied.scala b/tests/neg-deep-subtype/patmat-applied.scala
index 9123f3ab2ed6..fbdfdaf03626 100644
--- a/tests/neg-deep-subtype/patmat-applied.scala
+++ b/tests/neg-deep-subtype/patmat-applied.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class A[-T]
 class B[T] extends A[T]
diff --git a/tests/neg-macros/i9570.check b/tests/neg-macros/i9570.check
index 3c1f0f644318..23fba1b1c0a6 100644
--- a/tests/neg-macros/i9570.check
+++ b/tests/neg-macros/i9570.check
@@ -2,4 +2,4 @@
 15 |        case '{HCons(_,$t)} => // warn (in .check file)
    |                     ^
    |             Use of `_` for lambda in quoted pattern. Use explicit lambda instead or use `$_` to match any term.
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg-macros/i9570.scala b/tests/neg-macros/i9570.scala
index f1bae86fc17a..b77697ef477f 100644
--- a/tests/neg-macros/i9570.scala
+++ b/tests/neg-macros/i9570.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.quoted.*
 
@@ -25,4 +25,4 @@ object Macros {
   }
 }
 
-// nopos-error No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error No warnings can be incurred under -Werror
diff --git a/tests/neg-macros/macro-deprecation.check b/tests/neg-macros/macro-deprecation.check
index c3ba52b73c56..e091f5e701e9 100644
--- a/tests/neg-macros/macro-deprecation.check
+++ b/tests/neg-macros/macro-deprecation.check
@@ -2,4 +2,4 @@
 5 |inline def f = ${ impl } // warn (in .check file)
   |                  ^^^^
   |                  method impl is deprecated
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg-macros/macro-deprecation.scala b/tests/neg-macros/macro-deprecation.scala
index 7d44658bef90..61cefe91b78e 100644
--- a/tests/neg-macros/macro-deprecation.scala
+++ b/tests/neg-macros/macro-deprecation.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation
+//> using options -Werror -deprecation
 
 import scala.quoted.*
 
diff --git a/tests/neg-scalajs/enumeration-warnings.check b/tests/neg-scalajs/enumeration-warnings.check
index d092d545b22b..b388611645cd 100644
--- a/tests/neg-scalajs/enumeration-warnings.check
+++ b/tests/neg-scalajs/enumeration-warnings.check
@@ -58,4 +58,4 @@
    |                               ^^^^^^^^^^^^
    |                 Passing null as name to a constructor of scala.Enumeration.Val requires reflection at run-time.
    |                 The resulting program is unlikely to function properly.
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg-scalajs/enumeration-warnings.scala b/tests/neg-scalajs/enumeration-warnings.scala
index d05c044a32ab..bbf7ff8f357c 100644
--- a/tests/neg-scalajs/enumeration-warnings.scala
+++ b/tests/neg-scalajs/enumeration-warnings.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class UnableToTransformValue extends Enumeration {
   val a = {
diff --git a/tests/neg/IsInstanceOfClassTag.scala b/tests/neg/IsInstanceOfClassTag.scala
index 139ca7eae5a6..72d8c9224619 100644
--- a/tests/neg/IsInstanceOfClassTag.scala
+++ b/tests/neg/IsInstanceOfClassTag.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.reflect.ClassTag
 
diff --git a/tests/neg/adhoc-extension/B.scala b/tests/neg/adhoc-extension/B.scala
index 05a243077aaa..3287d21c4eea 100644
--- a/tests/neg/adhoc-extension/B.scala
+++ b/tests/neg/adhoc-extension/B.scala
@@ -1,4 +1,4 @@
-//> using options -source future -feature -Xfatal-warnings
+//> using options -source future -feature -Werror
 
 package adhoc
 class B extends A  // warn: adhoc-extension (under -strict -feature -Xfatal-warnings)
@@ -8,4 +8,4 @@ object O {
   val a = new A {}  // warn
   object E extends A  // warn
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/classtag-typetest/3_1-migration.scala b/tests/neg/classtag-typetest/3_1-migration.scala
index f387ccabf7c4..ddfcace194e4 100644
--- a/tests/neg/classtag-typetest/3_1-migration.scala
+++ b/tests/neg/classtag-typetest/3_1-migration.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.language.`future-migration`
 import scala.reflect.ClassTag
diff --git a/tests/neg/classtag-typetest/3_1.scala b/tests/neg/classtag-typetest/3_1.scala
index b6c8010364fc..2f5db79a6a25 100644
--- a/tests/neg/classtag-typetest/3_1.scala
+++ b/tests/neg/classtag-typetest/3_1.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.language.future
 import scala.reflect.ClassTag
diff --git a/tests/neg/enum-variance.scala b/tests/neg/enum-variance.scala
index ae6693ad94cc..75daa30a3c9c 100644
--- a/tests/neg/enum-variance.scala
+++ b/tests/neg/enum-variance.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 enum View[-T]:
   case Refl(f: T => T) // error: enum case Refl requires explicit declaration of type T
diff --git a/tests/neg/filtering-fors.scala b/tests/neg/filtering-fors.scala
index 7d998a37f057..d62a8722f4ba 100644
--- a/tests/neg/filtering-fors.scala
+++ b/tests/neg/filtering-fors.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 object Test {
 
@@ -31,4 +31,4 @@ object Test {
   for (case (x: String) <- xs; case (y, z) <- xs) do ()   // OK
 
   for (case (x, y) <- pairs) yield (y, x) // OK
-}
\ No newline at end of file
+}
diff --git a/tests/neg/i1050.scala b/tests/neg/i1050.scala
index 2489cbde49c9..5005521407b6 100644
--- a/tests/neg/i1050.scala
+++ b/tests/neg/i1050.scala
@@ -1,4 +1,4 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 // i1050 checks failing at posttyper
 trait A { type L <: Nothing }
diff --git a/tests/neg/i12188/Test.scala b/tests/neg/i12188/Test.scala
index 511a4804e5be..44403c8304b0 100644
--- a/tests/neg/i12188/Test.scala
+++ b/tests/neg/i12188/Test.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 sealed trait P
 case class PC1(a: String) extends P
@@ -10,4 +10,4 @@ def foo(x: P): Unit =
   x match           // warn
   case _: PC1 =>
 
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/i13946/BadPrinter.scala b/tests/neg/i13946/BadPrinter.scala
index f26ae97c1dfb..67ab6776a883 100644
--- a/tests/neg/i13946/BadPrinter.scala
+++ b/tests/neg/i13946/BadPrinter.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -feature
+//> using options -Werror -feature
 
 // in BadPrinter.scala
 import language.future
diff --git a/tests/neg/i15474b.check b/tests/neg/i15474b.check
index ac894168d51e..55974512acb5 100644
--- a/tests/neg/i15474b.check
+++ b/tests/neg/i15474b.check
@@ -3,4 +3,4 @@
   |                                   ^^^^^^^^^^
   |                                   Infinite loop in function body
   |                                   Test1.c.apply(from).toInt
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/i15474b.scala b/tests/neg/i15474b.scala
index 0a99056f8a6e..61ef0c4c0414 100644
--- a/tests/neg/i15474b.scala
+++ b/tests/neg/i15474b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.language.implicitConversions
 
diff --git a/tests/neg/i16092.scala b/tests/neg/i16092.scala
index c1327d3f6f70..3dcc7b31299c 100644
--- a/tests/neg/i16092.scala
+++ b/tests/neg/i16092.scala
@@ -1,4 +1,4 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 trait X {
   type T
diff --git a/tests/neg/i16876/Test.scala b/tests/neg/i16876/Test.scala
index dd7c1c2418ae..7bf582acaa37 100644
--- a/tests/neg/i16876/Test.scala
+++ b/tests/neg/i16876/Test.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Wunused:all
+//> using options -Werror -Wunused:all
 
 object Foo {
   private def myMethod(a: Int, b: Int, c: Int) = adder // ok
@@ -7,4 +7,4 @@ object Foo {
   private def myMethodFailing(a: Int, b: Int, c: Int) = a + 0 // warn // warn
   myMethodFailing(1, 2, 3)
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/i17335.scala b/tests/neg/i17335.scala
index b22ece6e42bf..021a2f190bbe 100644
--- a/tests/neg/i17335.scala
+++ b/tests/neg/i17335.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Wunused:all
+//> using options -Werror -Wunused:all
 
 def aMethod() =
   doStuff { (x) => x } // error
diff --git a/tests/neg/i17612b.check b/tests/neg/i17612b.check
index 681b682b459d..39e2738fcd63 100644
--- a/tests/neg/i17612b.check
+++ b/tests/neg/i17612b.check
@@ -30,4 +30,4 @@
 41 |	class UnderDerived(x: Int, y: Int, z: Int) extends Derived(x, 1, y, z) // warn // warn // warn
    |	                                   ^
    |	                                   value z in class UnderDerived shadows field z inherited from trait Base
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/i17612b/i17612b.scala b/tests/neg/i17612b/i17612b.scala
index a7afbf019d07..b833b37bb201 100644
--- a/tests/neg/i17612b/i17612b.scala
+++ b/tests/neg/i17612b/i17612b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Wshadow:private-shadow -source:3.3
+//> using options -Werror -Wshadow:private-shadow -source:3.3
 
 object i17612b:
 
@@ -42,4 +42,4 @@ object i17612b:
 
 	def main(args: Array[String]) =
 		val derived = new Derived(1, 1, 1, 1)
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/i17613b.check b/tests/neg/i17613b.check
index 494d218fb366..c1807d6c45cb 100644
--- a/tests/neg/i17613b.check
+++ b/tests/neg/i17613b.check
@@ -58,4 +58,4 @@
 42 |				class InnerCl[ImClassR] // warn
    |				              ^^^^^^^^
    |				              Type parameter ImClassR for class InnerCl shadows an explicitly renamed type : ImClassR
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/i17613b/i17613b.scala b/tests/neg/i17613b/i17613b.scala
index 0969a9a869ea..de854f9e43b9 100644
--- a/tests/neg/i17613b/i17613b.scala
+++ b/tests/neg/i17613b/i17613b.scala
@@ -1,4 +1,4 @@
-//> using options -Wshadow:type-parameter-shadow -Xfatal-warnings
+//> using options -Wshadow:type-parameter-shadow -Werror
 
 object i17613b:
 	import importTry._
diff --git a/tests/neg/i18632.check b/tests/neg/i18632.check
index a0fa733cf8e3..f5b128dd39a3 100644
--- a/tests/neg/i18632.check
+++ b/tests/neg/i18632.check
@@ -2,4 +2,4 @@
 12 |  bar // warn
    |  ^^^
    |  unused value of type String
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/i4986d.scala b/tests/neg/i4986d.scala
index 0def343fe847..36b6c54d9753 100644
--- a/tests/neg/i4986d.scala
+++ b/tests/neg/i4986d.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 trait Foo[A]
 
@@ -22,4 +22,4 @@ trait Bar[A]
 type Barable[A] = {
   def bar(implicit ev: Bar[A]): Any // ok
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/i5854.scala b/tests/neg/i5854.scala
index 61c7c2d833e7..f67216669c66 100644
--- a/tests/neg/i5854.scala
+++ b/tests/neg/i5854.scala
@@ -1,4 +1,4 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 object bar {
   trait Sub {
@@ -23,4 +23,4 @@ object bar {
     val zero : String = (new Caster[Int,String]()).upcast(0)
     println("...")
   }
-}
\ No newline at end of file
+}
diff --git a/tests/neg/i6716-source-3.4.scala b/tests/neg/i6716-source-3.4.scala
index f6f1961b67a4..966a45ca9eb2 100644
--- a/tests/neg/i6716-source-3.4.scala
+++ b/tests/neg/i6716-source-3.4.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -source 3.4
+//> using options -Werror -source 3.4
 
 trait Monad[T]:
   def id: String
@@ -16,4 +16,4 @@ object Test extends App {
   println(summon[Monad[Foo]].id)
   println(summon[Monad[Bar]].id)
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/i8681.scala b/tests/neg/i8681.scala
index 637dd123bd48..fcde4b3d8e34 100644
--- a/tests/neg/i8681.scala
+++ b/tests/neg/i8681.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 case class A(a: Int)
 case class B(b: Int)
@@ -14,4 +14,4 @@ val b = (A(1): A | B) match {
   case B(_) => "OK"
   case C(_) => "NOT OK" // error
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/i8711.check b/tests/neg/i8711.check
index 245092a6dfd0..492d16dfa1db 100644
--- a/tests/neg/i8711.check
+++ b/tests/neg/i8711.check
@@ -18,4 +18,4 @@
 14 |    case x: C => x // error
    |         ^
    |         this case is unreachable since type A | B and class C are unrelated
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/i8711.scala b/tests/neg/i8711.scala
index 18f53447d024..88b0a39839fd 100644
--- a/tests/neg/i8711.scala
+++ b/tests/neg/i8711.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class A
 class B
@@ -21,4 +21,4 @@ object Test {
   }
 }
 
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/i9168.scala b/tests/neg/i9168.scala
index ed8bd4750972..b8da818e58b7 100644
--- a/tests/neg/i9168.scala
+++ b/tests/neg/i9168.scala
@@ -1,3 +1,3 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 def g: Int = try 42 finally ; // error
diff --git a/tests/neg/i9408b.check b/tests/neg/i9408b.check
index 1fd651f70112..6672e66d4f08 100644
--- a/tests/neg/i9408b.check
+++ b/tests/neg/i9408b.check
@@ -2,4 +2,4 @@
 8 |  val length: Int = "abc" // warn
   |                    ^^^^^
   |The conversion (test.conversions.Conv.implicitLength : String => Int) will not be applied implicitly here in Scala 3 because only implicit methods and instances of Conversion class will continue to work as implicit views.
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/i9408b/Test_2.scala b/tests/neg/i9408b/Test_2.scala
index dc5c2bd7b30d..3e5170a9b58e 100644
--- a/tests/neg/i9408b/Test_2.scala
+++ b/tests/neg/i9408b/Test_2.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import language.`3.0-migration`
 import scala.language.implicitConversions
@@ -8,4 +8,4 @@ object Test {
   val length: Int = "abc" // warn
 }
 
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/impl-conv/B.scala b/tests/neg/impl-conv/B.scala
index 7ba9fbb92459..fb35add21cd9 100644
--- a/tests/neg/impl-conv/B.scala
+++ b/tests/neg/impl-conv/B.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -feature
+//> using options -Werror -feature
 
 package implConv
 
@@ -10,4 +10,4 @@ object B {
   val x: Int = ""  // ok
   val y: String = 1 // warn: feature
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/indentLeft.scala b/tests/neg/indentLeft.scala
index 22386bd54561..dd47463ae959 100644
--- a/tests/neg/indentLeft.scala
+++ b/tests/neg/indentLeft.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 // nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
 
 object Test {
@@ -8,4 +8,4 @@ object Test {
 
   println("!")  // warn: too far to the left
 }
-// error: too far to the left
\ No newline at end of file
+// error: too far to the left
diff --git a/tests/neg/indentRight.scala b/tests/neg/indentRight.scala
index e3359bf238dd..4bddd19a513e 100644
--- a/tests/neg/indentRight.scala
+++ b/tests/neg/indentRight.scala
@@ -1,4 +1,4 @@
-//> using options -no-indent -Xfatal-warnings
+//> using options -no-indent -Werror
 
 trait A
     case class B() extends A  // warn: Line is indented too far to the right
@@ -33,4 +33,4 @@ object Test {
 
   println("!")  // error: expected a toplevel definition
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/inline-unstable-accessors.check b/tests/neg/inline-unstable-accessors.check
index c1984e4cc533..deab0b898ccc 100644
--- a/tests/neg/inline-unstable-accessors.check
+++ b/tests/neg/inline-unstable-accessors.check
@@ -297,4 +297,4 @@
    | added to package I:
    |   @publicInBinary private[I] def inline$valBinaryAPI2: Int = foo.I.valBinaryAPI2
     --------------------------------------------------------------------------------------------------------------------
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/into-override.scala b/tests/neg/into-override.scala
index 6a1e2ca10fda..f5f6db4da169 100644
--- a/tests/neg/into-override.scala
+++ b/tests/neg/into-override.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -preview
+//> using options -Werror -preview
 
 import Conversion.into
 
diff --git a/tests/neg/missing-targetName.scala b/tests/neg/missing-targetName.scala
index 32f4646cd5a3..25c3ede1ed14 100644
--- a/tests/neg/missing-targetName.scala
+++ b/tests/neg/missing-targetName.scala
@@ -1,4 +1,4 @@
-//> using options -Yrequire-targetName -Xfatal-warnings
+//> using options -Yrequire-targetName -Werror
 
 // Compile with -strict -Xfatal-warnings -deprecation
 import scala.annotation.targetName
@@ -9,4 +9,4 @@ class & {   // error
   val frozen_& : Int = ???  // warn
   object some_???           // warn
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/nullless.scala b/tests/neg/nullless.scala
index 20f9af841e14..662d5cab4a03 100644
--- a/tests/neg/nullless.scala
+++ b/tests/neg/nullless.scala
@@ -1,4 +1,4 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 object nullless {
   trait LowerBound[T] {
diff --git a/tests/neg/pureStatement.scala b/tests/neg/pureStatement.scala
index 09a59f1621db..12e6af81b346 100644
--- a/tests/neg/pureStatement.scala
+++ b/tests/neg/pureStatement.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class IOCapability
 
@@ -32,4 +32,4 @@ object Test {
   broken.foo // no extra error, and no pure expression warning
   broken.foo() // same
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/runtimeChecked-2.check b/tests/neg/runtimeChecked-2.check
index 1b30d637a6b9..317836588ff9 100644
--- a/tests/neg/runtimeChecked-2.check
+++ b/tests/neg/runtimeChecked-2.check
@@ -2,4 +2,4 @@
 10 |      case is: Some[t] => ??? // unreachable
    |           ^^^^^^^^^^^
    |           Unreachable case
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/runtimeChecked.check b/tests/neg/runtimeChecked.check
index 3d984e08517d..faa0971a0e3b 100644
--- a/tests/neg/runtimeChecked.check
+++ b/tests/neg/runtimeChecked.check
@@ -4,4 +4,4 @@
    |the type test for ::[Int] cannot be checked at runtime because its type arguments can't be determined from List[Any]
    |
    | longer explanation available when compiling with `-explain`
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/structural-2.scala b/tests/neg/structural-2.scala
index 4353467fc821..e340b36d60ce 100644
--- a/tests/neg/structural-2.scala
+++ b/tests/neg/structural-2.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.reflect.Selectable.reflectiveSelectable
 
diff --git a/tests/neg/unchecked-patterns.scala b/tests/neg/unchecked-patterns.scala
index d0e04be687dc..f77ab8a9a263 100644
--- a/tests/neg/unchecked-patterns.scala
+++ b/tests/neg/unchecked-patterns.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 object Test {
 
@@ -25,4 +25,4 @@ object Test {
   val Pair(t1, t2) = (5, 5)          // OK
   val Triple(u1, u2, u3) = (5, 5, 5) // OK
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
\ No newline at end of file
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/pos-deep-subtype/3324c.scala b/tests/pos-deep-subtype/3324c.scala
index aefa25eaafc2..58c008c9dbd9 100644
--- a/tests/pos-deep-subtype/3324c.scala
+++ b/tests/pos-deep-subtype/3324c.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 sealed trait A[T]
 class B[T] extends A[T]
diff --git a/tests/pos-deep-subtype/3324d.scala b/tests/pos-deep-subtype/3324d.scala
index 9372f33c3d10..d53f4acc90e7 100644
--- a/tests/pos-deep-subtype/3324d.scala
+++ b/tests/pos-deep-subtype/3324d.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class Test {
   val x: Any = ???
@@ -7,4 +7,4 @@ class Test {
     case _: List[Int @unchecked] => 5
     case _: Option[Int] @unchecked => 5
   }
-}
\ No newline at end of file
+}
diff --git a/tests/pos-deep-subtype/3324e.scala b/tests/pos-deep-subtype/3324e.scala
index 58ba0152ed21..38bbe98af866 100644
--- a/tests/pos-deep-subtype/3324e.scala
+++ b/tests/pos-deep-subtype/3324e.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class C[T] {
   val x: T = ???
diff --git a/tests/pos-deep-subtype/3324h.scala b/tests/pos-deep-subtype/3324h.scala
index 6bae5f6a01d9..dfd210990c75 100644
--- a/tests/pos-deep-subtype/3324h.scala
+++ b/tests/pos-deep-subtype/3324h.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.language.`3.3`
 
diff --git a/tests/pos-deep-subtype/Result.scala b/tests/pos-deep-subtype/Result.scala
index df42e54f3138..3509e4db53ef 100644
--- a/tests/pos-deep-subtype/Result.scala
+++ b/tests/pos-deep-subtype/Result.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 object p {
 
diff --git a/tests/pos-deep-subtype/classTag.scala b/tests/pos-deep-subtype/classTag.scala
index b084f7f7e59c..5433e3edbf12 100644
--- a/tests/pos-deep-subtype/classTag.scala
+++ b/tests/pos-deep-subtype/classTag.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.reflect.ClassTag
 
@@ -9,4 +9,4 @@ object IsInstanceOfClassTag {
       case _ => None
     }
   }
-}
\ No newline at end of file
+}
diff --git a/tests/pos-deep-subtype/gadt.scala b/tests/pos-deep-subtype/gadt.scala
index 18fbe6e10986..4d8bf9cb1a08 100644
--- a/tests/pos-deep-subtype/gadt.scala
+++ b/tests/pos-deep-subtype/gadt.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 sealed trait Exp[T]
 case class Num(n: Int) extends Exp[Int]
diff --git a/tests/pos-deep-subtype/i16899.scala b/tests/pos-deep-subtype/i16899.scala
index e5acac1f927e..2b4f8a063c84 100644
--- a/tests/pos-deep-subtype/i16899.scala
+++ b/tests/pos-deep-subtype/i16899.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 sealed trait Unset
 
diff --git a/tests/pos-deep-subtype/i9736.scala b/tests/pos-deep-subtype/i9736.scala
index 6ef1c42c981e..025f4c6d2db6 100644
--- a/tests/pos-deep-subtype/i9736.scala
+++ b/tests/pos-deep-subtype/i9736.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class Test {
   type MyCombo = Int | Unit
@@ -6,4 +6,4 @@ class Test {
    z match
     case i: Int => ???
     case _ => ???
-}
\ No newline at end of file
+}
diff --git a/tests/pos-deep-subtype/i9782.scala b/tests/pos-deep-subtype/i9782.scala
index 02c69a35b752..f9d093079e24 100644
--- a/tests/pos-deep-subtype/i9782.scala
+++ b/tests/pos-deep-subtype/i9782.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 trait Txn[T <: Txn[T]]
 
diff --git a/tests/pos-macros/i13405/Test.scala b/tests/pos-macros/i13405/Test.scala
index b698bd875642..6a5d5c638707 100644
--- a/tests/pos-macros/i13405/Test.scala
+++ b/tests/pos-macros/i13405/Test.scala
@@ -1,3 +1,3 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 @main def main: Unit = hh()
diff --git a/tests/pos-macros/i21672/Test_2.scala b/tests/pos-macros/i21672/Test_2.scala
index b164962100af..b1d06411b1aa 100644
--- a/tests/pos-macros/i21672/Test_2.scala
+++ b/tests/pos-macros/i21672/Test_2.scala
@@ -1,3 +1,3 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 object Test:
   Repro()
diff --git a/tests/pos/Dynamic.scala b/tests/pos/Dynamic.scala
index 9f3a83468fc1..568a05d55ea6 100644
--- a/tests/pos/Dynamic.scala
+++ b/tests/pos/Dynamic.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 package scala
 
diff --git a/tests/pos/adhoc-extension/A.scala b/tests/pos/adhoc-extension/A.scala
index efc0415cdc15..428b80a10bf6 100644
--- a/tests/pos/adhoc-extension/A.scala
+++ b/tests/pos/adhoc-extension/A.scala
@@ -1,4 +1,4 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 package adhoc
 class A
diff --git a/tests/pos/annot-constant/Test_2.scala b/tests/pos/annot-constant/Test_2.scala
index 420b33195a45..cd58ed099d98 100644
--- a/tests/pos/annot-constant/Test_2.scala
+++ b/tests/pos/annot-constant/Test_2.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 package pkg
 
diff --git a/tests/pos/given-loop-prevention.scala b/tests/pos/given-loop-prevention.scala
index f02559af1e82..0aab22dc3233 100644
--- a/tests/pos/given-loop-prevention.scala
+++ b/tests/pos/given-loop-prevention.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -source 3.4
+//> using options -Werror -source 3.4
 
 class Foo
 
diff --git a/tests/pos/i10247.scala b/tests/pos/i10247.scala
index 4268e309a4ae..496bba3df95a 100644
--- a/tests/pos/i10247.scala
+++ b/tests/pos/i10247.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 // check that deprecation warnings of Red are not caught in its enclosing scope
 enum Color(rgb: Int) {
diff --git a/tests/pos/i10259.scala b/tests/pos/i10259.scala
index e8da9e6a7be7..f3a223391e6d 100644
--- a/tests/pos/i10259.scala
+++ b/tests/pos/i10259.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 trait S[T] extends (T => T):
   def apply(x: T) = ???
diff --git a/tests/pos/i10383.scala b/tests/pos/i10383.scala
index f14267a38041..5e827bbfba9f 100644
--- a/tests/pos/i10383.scala
+++ b/tests/pos/i10383.scala
@@ -1,3 +1,3 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 def r = BigInt(1) to BigInt(3) // error
diff --git a/tests/pos/i11729.scala b/tests/pos/i11729.scala
index 79d3174dc2e9..933ddf387067 100644
--- a/tests/pos/i11729.scala
+++ b/tests/pos/i11729.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 type Return[X] = X match
     case List[t] => List[t]
diff --git a/tests/pos/i13433.scala b/tests/pos/i13433.scala
index c38199e3b917..90b5b1cd718f 100644
--- a/tests/pos/i13433.scala
+++ b/tests/pos/i13433.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import scala.reflect.TypeTest
 
diff --git a/tests/pos/i13433b.scala b/tests/pos/i13433b.scala
index e8316f92e330..9ef86d0c5e24 100644
--- a/tests/pos/i13433b.scala
+++ b/tests/pos/i13433b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import scala.reflect.ClassTag
 
diff --git a/tests/pos/i14637.scala b/tests/pos/i14637.scala
index 512471f7b19a..debeacf0464b 100644
--- a/tests/pos/i14637.scala
+++ b/tests/pos/i14637.scala
@@ -1,8 +1,8 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 class C
 
 object Givens:
   given cOrdering: Ordering[C]:
     override def compare(c0: C, c1: C) = 0
-  val greeting = "we love Givens"
\ No newline at end of file
+  val greeting = "we love Givens"
diff --git a/tests/pos/i15166/Test_2.scala b/tests/pos/i15166/Test_2.scala
index b447aacde2ab..55056d00be30 100644
--- a/tests/pos/i15166/Test_2.scala
+++ b/tests/pos/i15166/Test_2.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 object Test {
   val x: InterfaceAudience_JAVA_ONLY_1.Public = ???
 }
diff --git a/tests/pos/i15474.scala b/tests/pos/i15474.scala
index f2c85120e4b2..20603f397b7c 100644
--- a/tests/pos/i15474.scala
+++ b/tests/pos/i15474.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 import scala.language.implicitConversions
 import scala.language.future
 
diff --git a/tests/pos/i16649-irrefutable.scala b/tests/pos/i16649-irrefutable.scala
index 7a5a98733922..45ef4265ccbd 100644
--- a/tests/pos/i16649-irrefutable.scala
+++ b/tests/pos/i16649-irrefutable.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import quoted.*
 
diff --git a/tests/pos/i16808.scala b/tests/pos/i16808.scala
index 43e77634a535..d0bc55b43316 100644
--- a/tests/pos/i16808.scala
+++ b/tests/pos/i16808.scala
@@ -1,4 +1,4 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 def collectKeys[A, B, C](xs: Map[A, B])(f: PartialFunction[A, C]): Map[C, B] =
 	xs.collect{ case (f(c) , b) => (c, b) }
diff --git a/tests/pos/i17735.scala b/tests/pos/i17735.scala
index 17fb31010a8a..2927eabadd68 100644
--- a/tests/pos/i17735.scala
+++ b/tests/pos/i17735.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Wvalue-discard
+//> using options -Werror -Wvalue-discard
 
 import scala.collection.mutable
 import scala.annotation.nowarn
diff --git a/tests/pos/i17735a.scala b/tests/pos/i17735a.scala
index b4d91f8d25fc..c698be537451 100644
--- a/tests/pos/i17735a.scala
+++ b/tests/pos/i17735a.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Wvalue-discard -Wconf:msg=non-Unit:s
+//> using options -Werror -Wvalue-discard -Wconf:msg=non-Unit:s
 
 import scala.collection.mutable
 import scala.annotation.nowarn
diff --git a/tests/pos/i17741.scala b/tests/pos/i17741.scala
index aa32e5a573d4..e22a1f0a882d 100644
--- a/tests/pos/i17741.scala
+++ b/tests/pos/i17741.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Wnonunit-statement
+//> using options -Werror -Wnonunit-statement
 
 class Node()
 class Elem(
diff --git a/tests/pos/i19013-a.scala b/tests/pos/i19013-a.scala
index 0a6a5e2d1179..afc785f349e5 100644
--- a/tests/pos/i19013-a.scala
+++ b/tests/pos/i19013-a.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 def handle[E <: Exception](f: => Unit): Option[E] =
   try
diff --git a/tests/pos/i19013-b.scala b/tests/pos/i19013-b.scala
index a4ec71654ff5..80240300783b 100644
--- a/tests/pos/i19013-b.scala
+++ b/tests/pos/i19013-b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 case class CustomException(x: Any) extends Exception("")
 
@@ -8,4 +8,4 @@ def handle[E](f: => Unit): Option[E] =
     None
   catch case CustomException(e: E @unchecked ) => Some(e)
 
-val r: RuntimeException = handle[RuntimeException](throw new Exception()).get
\ No newline at end of file
+val r: RuntimeException = handle[RuntimeException](throw new Exception()).get
diff --git a/tests/pos/i19301.scala b/tests/pos/i19301.scala
index a4a5a858b754..ea0549313cb0 100644
--- a/tests/pos/i19301.scala
+++ b/tests/pos/i19301.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 object Extensions:
   infix def foo(x: String): Unit = ()
diff --git a/tests/pos/i21282.scala b/tests/pos/i21282.scala
index a483f3763f89..a2648b1bf0ec 100644
--- a/tests/pos/i21282.scala
+++ b/tests/pos/i21282.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -source:future-migration
+//> using options -Werror -source:future-migration
 
 import scala.quoted.*
 
diff --git a/tests/pos/i21749.scala b/tests/pos/i21749.scala
index 6180b629f06b..1b3d54d26768 100644
--- a/tests/pos/i21749.scala
+++ b/tests/pos/i21749.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -no-indent
+//> using options -Werror -no-indent
 
 object Test {
   1 match {
diff --git a/tests/pos/i2673.scala b/tests/pos/i2673.scala
index cb426cd6be0f..9544f2004bbf 100644
--- a/tests/pos/i2673.scala
+++ b/tests/pos/i2673.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 package Foos
 
diff --git a/tests/pos/i3323b.scala b/tests/pos/i3323b.scala
index 0edc6177bbe9..f912ddea1dad 100644
--- a/tests/pos/i3323b.scala
+++ b/tests/pos/i3323b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 class Foo {
   def foo(lss: List[Int]): Unit = {
diff --git a/tests/pos/i3589b.scala b/tests/pos/i3589b.scala
index f4552c7f8370..4d7189335ddc 100644
--- a/tests/pos/i3589b.scala
+++ b/tests/pos/i3589b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 class Test {
   def test(x: 1 | 2 | 3) = (x: @annotation.switch) match {
diff --git a/tests/pos/i4166.scala b/tests/pos/i4166.scala
index 2ce9d018b614..8d6042294fa9 100644
--- a/tests/pos/i4166.scala
+++ b/tests/pos/i4166.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 package foo {
   class Hello
diff --git a/tests/pos/i4185.scala b/tests/pos/i4185.scala
index 643f479c59b6..631379e125d1 100644
--- a/tests/pos/i4185.scala
+++ b/tests/pos/i4185.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 object ord {
   class Ord
diff --git a/tests/pos/i4674.scala b/tests/pos/i4674.scala
index 3b570a74e80a..228debabc902 100644
--- a/tests/pos/i4674.scala
+++ b/tests/pos/i4674.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 class Test {
   def test(x: String) = {
diff --git a/tests/pos/i5970.scala b/tests/pos/i5970.scala
index 668e42cbbad5..e287924e7b2a 100644
--- a/tests/pos/i5970.scala
+++ b/tests/pos/i5970.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 object Test {
   case class Foo[T](t: T)
diff --git a/tests/pos/i6190a.scala b/tests/pos/i6190a.scala
index b6d21662389e..41a98459714c 100644
--- a/tests/pos/i6190a.scala
+++ b/tests/pos/i6190a.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 case class Rule(name: String)
 object Rule extends (String => Rule) {
diff --git a/tests/pos/i6190c.scala b/tests/pos/i6190c.scala
index 37a837addb62..45a6738d0ca9 100644
--- a/tests/pos/i6190c.scala
+++ b/tests/pos/i6190c.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 case class Rule(name: String)
 
diff --git a/tests/pos/i6290.scala b/tests/pos/i6290.scala
index bc3646f1e1d2..ce125e6ae572 100644
--- a/tests/pos/i6290.scala
+++ b/tests/pos/i6290.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature -source:3.3
+//> using options -Werror -deprecation -feature -source:3.3
 
 class TC { type T }
 
diff --git a/tests/pos/i6621.scala b/tests/pos/i6621.scala
index 599a75ba776e..33d3697aeb19 100644
--- a/tests/pos/i6621.scala
+++ b/tests/pos/i6621.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 object Unapply {
   def unapply(a: Any): Option[(Int, Int)] =
diff --git a/tests/pos/i7219b.scala b/tests/pos/i7219b.scala
index 91dc0d136420..a31196f0eba5 100644
--- a/tests/pos/i7219b.scala
+++ b/tests/pos/i7219b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 object Foo {
   enum MyEnum {
diff --git a/tests/pos/i7219c.scala b/tests/pos/i7219c.scala
index 1ddfeca39ff1..3c23a3f935d2 100644
--- a/tests/pos/i7219c.scala
+++ b/tests/pos/i7219c.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 object Foo {
   enum MyEnum {
diff --git a/tests/pos/i7296.scala b/tests/pos/i7296.scala
index 67fb3eee48a4..37c40bec8369 100644
--- a/tests/pos/i7296.scala
+++ b/tests/pos/i7296.scala
@@ -1,4 +1,4 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 class Foo:
   private var blah: Double = 0L
diff --git a/tests/pos/i8758.scala b/tests/pos/i8758.scala
index ad170750c09e..1ac40d454ace 100644
--- a/tests/pos/i8758.scala
+++ b/tests/pos/i8758.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 def test = "?johndoe" match {
   case s":$name" => println(s":name $name")
diff --git a/tests/pos/i8781.scala b/tests/pos/i8781.scala
index 857ff43b9c0a..54db47f37086 100644
--- a/tests/pos/i8781.scala
+++ b/tests/pos/i8781.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 @main
 def Test =
diff --git a/tests/pos/i8956.scala b/tests/pos/i8956.scala
index a6937a3f2363..40fec732a9c3 100644
--- a/tests/pos/i8956.scala
+++ b/tests/pos/i8956.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 type Numeric = Double | Int
 
diff --git a/tests/pos/i9260.scala b/tests/pos/i9260.scala
index cf740eb3c096..2879c4b94989 100644
--- a/tests/pos/i9260.scala
+++ b/tests/pos/i9260.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 package asts
 
diff --git a/tests/pos/i9751.scala b/tests/pos/i9751.scala
index 78c9116f77d1..284239293f51 100644
--- a/tests/pos/i9751.scala
+++ b/tests/pos/i9751.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 object Test {
   extension (x: Int)
diff --git a/tests/pos/i9751b.scala b/tests/pos/i9751b.scala
index bbbe8052a20c..9cb3700327a1 100644
--- a/tests/pos/i9751b.scala
+++ b/tests/pos/i9751b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 object Test {
   inline def f(inline x: Boolean): Unit =
diff --git a/tests/pos/i9776.scala b/tests/pos/i9776.scala
index 73efe2531918..ebcf585a5ef3 100644
--- a/tests/pos/i9776.scala
+++ b/tests/pos/i9776.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import scala.annotation.switch
 
diff --git a/tests/pos/i9804.scala b/tests/pos/i9804.scala
index 80b0de79b97f..8d96bbdcfacc 100644
--- a/tests/pos/i9804.scala
+++ b/tests/pos/i9804.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import scala.quoted.*
 
diff --git a/tests/pos/into-expr.scala b/tests/pos/into-expr.scala
index 8fd1a13fbfee..ecb057622f32 100644
--- a/tests/pos/into-expr.scala
+++ b/tests/pos/into-expr.scala
@@ -1,5 +1,5 @@
 
-//> using options -feature -Xfatal-warnings -preview
+//> using options -feature -Werror -preview
 
 import Conversion.into
 
diff --git a/tests/pos/into-sam.scala b/tests/pos/into-sam.scala
index bb12696b9fc6..c887a824f2b8 100644
--- a/tests/pos/into-sam.scala
+++ b/tests/pos/into-sam.scala
@@ -1,5 +1,5 @@
 
-//> using options -feature -Xfatal-warnings -preview
+//> using options -feature -Werror -preview
 
 import Conversion.into
 
diff --git a/tests/pos/matchable-same-type.scala b/tests/pos/matchable-same-type.scala
index 71ab788d0d16..3d6ecb51bf2b 100644
--- a/tests/pos/matchable-same-type.scala
+++ b/tests/pos/matchable-same-type.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import scala.language.`future-migration`
 
diff --git a/tests/pos/not-looping-implicit.scala b/tests/pos/not-looping-implicit.scala
index d99da915fbf4..4a231a8ebf8f 100644
--- a/tests/pos/not-looping-implicit.scala
+++ b/tests/pos/not-looping-implicit.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import scala.deriving.Mirror
 import scala.compiletime._
@@ -42,4 +42,4 @@ object InputValue {
 
 @main def Test =
   implicit lazy val inputValueSchema: Schema[InputValue] = Schema.gen
-  println(summon[Schema[InputValue]])
\ No newline at end of file
+  println(summon[Schema[InputValue]])
diff --git a/tests/pos/nowarnannot.scala b/tests/pos/nowarnannot.scala
index 1710ae34b56f..eb4ca27ef7d3 100644
--- a/tests/pos/nowarnannot.scala
+++ b/tests/pos/nowarnannot.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Wvalue-discard
+//> using options -Werror -Wvalue-discard
 
 case class F(i: Int)
 
diff --git a/tests/pos/stats-in-empty-pkg.scala b/tests/pos/stats-in-empty-pkg.scala
index cbfade71f8b9..a6d43006341e 100644
--- a/tests/pos/stats-in-empty-pkg.scala
+++ b/tests/pos/stats-in-empty-pkg.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 def foo = 23
 val bar = foo
diff --git a/tests/pos/strict-pattern-bindings-3.0-migration.scala b/tests/pos/strict-pattern-bindings-3.0-migration.scala
index f1d88af0c152..3cb9d2c5f485 100644
--- a/tests/pos/strict-pattern-bindings-3.0-migration.scala
+++ b/tests/pos/strict-pattern-bindings-3.0-migration.scala
@@ -1,6 +1,6 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
-// These tests should pass under -Xfatal-warnings with source version less than 3.2
+// These tests should pass under -Werror with source version less than 3.2
 import language.`3.0-migration`
 
 object Test:
diff --git a/tests/pos/strict-pattern-bindings-3.1.scala b/tests/pos/strict-pattern-bindings-3.1.scala
index bb912204e38a..a4deff26d5db 100644
--- a/tests/pos/strict-pattern-bindings-3.1.scala
+++ b/tests/pos/strict-pattern-bindings-3.1.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 // These tests should pass under -Xfatal-warnings with source version less than 3.2
 import language.`3.1`
diff --git a/tests/pos/switches.scala b/tests/pos/switches.scala
index beb378debb40..4e6770ca8b46 100644
--- a/tests/pos/switches.scala
+++ b/tests/pos/switches.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import scala.annotation.switch
 
diff --git a/tests/pos/t6595.scala b/tests/pos/t6595.scala
index b89c8f97308f..3ae9f44e50d3 100644
--- a/tests/pos/t6595.scala
+++ b/tests/pos/t6595.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import scala.annotation.switch
 
diff --git a/tests/pos/t6963c.scala b/tests/pos/t6963c.scala
index 6effd4082065..156af48ef857 100644
--- a/tests/pos/t6963c.scala
+++ b/tests/pos/t6963c.scala
@@ -1,4 +1,4 @@
-//> using options -Xmigration:2.9 -Xfatal-warnings
+//> using options -Xmigration:2.9 -Werror
 //
 import collection.Seq
 object Test {
diff --git a/tests/pos/tasty-parent-unapply.scala b/tests/pos/tasty-parent-unapply.scala
index 0f882ee060d8..10eab77ea6b0 100644
--- a/tests/pos/tasty-parent-unapply.scala
+++ b/tests/pos/tasty-parent-unapply.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import scala.quoted.*
 
diff --git a/tests/pos/type-test-matchable.scala b/tests/pos/type-test-matchable.scala
index 579af12fa2e7..f6a937a9c985 100644
--- a/tests/pos/type-test-matchable.scala
+++ b/tests/pos/type-test-matchable.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 import scala.language.`future-migration`
 import scala.reflect.TypeTest
diff --git a/tests/pos/unchecked-scrutinee.scala b/tests/pos/unchecked-scrutinee.scala
index 72fcd3da14e4..b446a2b8b954 100644
--- a/tests/pos/unchecked-scrutinee.scala
+++ b/tests/pos/unchecked-scrutinee.scala
@@ -1,7 +1,7 @@
-//> using options -Xfatal-warnings -deprecation -feature
+//> using options -Werror -deprecation -feature
 
 object Test {
   (List(1: @unchecked, 2, 3): @unchecked) match {
     case a :: as =>
   }
-}
\ No newline at end of file
+}
diff --git a/tests/pos/xfatalWarnings.scala b/tests/pos/xfatalWarnings.scala
index ba278fc87aa3..c34c23a883dc 100644
--- a/tests/pos/xfatalWarnings.scala
+++ b/tests/pos/xfatalWarnings.scala
@@ -1,4 +1,4 @@
-//> using options -nowarn -Xfatal-warnings
+//> using options -nowarn -Werror
 // succeeds despite -Xfatal-warnings because of -nowarn
 
 object xfatalWarnings {
diff --git a/tests/run/convertible.scala b/tests/run/convertible.scala
index bf1a41234b17..4525e52e654e 100644
--- a/tests/run/convertible.scala
+++ b/tests/run/convertible.scala
@@ -1,4 +1,4 @@
-//> using options -feature -Xfatal-warnings -preview
+//> using options -feature -Werror -preview
 
 import Conversion.into
 
diff --git a/tests/run/i11050.scala b/tests/run/i11050.scala
index 34613fdaf5fd..b5d1df16b14d 100644
--- a/tests/run/i11050.scala
+++ b/tests/run/i11050.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.compiletime.*
 import scala.deriving.*
diff --git a/tests/run/i6716.scala b/tests/run/i6716.scala
index c0678c51fb30..db67bf4325a6 100644
--- a/tests/run/i6716.scala
+++ b/tests/run/i6716.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 trait Monad[T]:
   def id: String
@@ -15,4 +15,4 @@ object Bar {
 object Test extends App {
   println(summon[Monad[Foo]].id)
   println(summon[Monad[Bar]].id)
-}
\ No newline at end of file
+}
diff --git a/tests/warn/implicit-conversions-old.scala b/tests/warn/implicit-conversions-old.scala
index 24e1124015e3..9781fb16f61d 100644
--- a/tests/warn/implicit-conversions-old.scala
+++ b/tests/warn/implicit-conversions-old.scala
@@ -5,15 +5,15 @@ class B
 
 object A {
 
-  implicit def a2b(x: A): B = ??? // warn under -Xfatal-warnings -feature
+  implicit def a2b(x: A): B = ??? // warn under -Werror -feature
 
-  implicit def b2a(x: B): A = ??? // warn under -Xfatal-warnings -feature
+  implicit def b2a(x: B): A = ??? // warn under -Werror -feature
 }
 
 class C
 
 object D {
-  implicit def a2c(x: A): C = ??? // warn under -Xfatal-warnings -feature
+  implicit def a2c(x: A): C = ??? // warn under -Werror -feature
 }
 
 object Test {
@@ -22,4 +22,4 @@ object Test {
   val x1: A = new B
   val x2: B = new A  // ok, since it's an old-style comversion
   val x3: C = new A  // ok, since it's an old-style comversion
-}
\ No newline at end of file
+}
diff --git a/tests/warn/implicit-conversions.scala b/tests/warn/implicit-conversions.scala
index 2896d7dc4447..b6db0dc4f270 100644
--- a/tests/warn/implicit-conversions.scala
+++ b/tests/warn/implicit-conversions.scala
@@ -25,7 +25,7 @@ object D {
 object Test {
   import D.given
 
-  val x1: A = new B  // warn under -Xfatal-warnings -feature
-  val x2: B = new A  // warn under -Xfatal-warnings -feature
-  val x3: C = new A  // warn under -Xfatal-warnings -feature
-}
\ No newline at end of file
+  val x1: A = new B  // warn under -Werror -feature
+  val x2: B = new A  // warn under -Werror -feature
+  val x3: C = new A  // warn under -Werror -feature
+}
diff --git a/tests/warn/strict-pattern-bindings-3.2.scala b/tests/warn/strict-pattern-bindings-3.2.scala
index e4df8e770a01..beb2e4d6a771 100644
--- a/tests/warn/strict-pattern-bindings-3.2.scala
+++ b/tests/warn/strict-pattern-bindings-3.2.scala
@@ -1,5 +1,5 @@
 
-// These tests should fail under -Xfatal-warnings with source version source version 3.2 or later
+// These tests should fail under -Werror with source version source version 3.2 or later
 import language.`3.2`
 
 object Test:
@@ -34,4 +34,4 @@ object Test:
   object Triple { def unapply(t: (Int, Int, Int)): (Int, Int, Int) = t }
 
   val Positive(p) = 5                // warn
-  val Some(s1) = Option(1)           // warn
\ No newline at end of file
+  val Some(s1) = Option(1)           // warn