diff --git a/sjsonnet/src/sjsonnet/ByteRenderer.scala b/sjsonnet/src/sjsonnet/ByteRenderer.scala
index 7eb8656f..2287f641 100644
--- a/sjsonnet/src/sjsonnet/ByteRenderer.scala
+++ b/sjsonnet/src/sjsonnet/ByteRenderer.scala
@@ -391,7 +391,7 @@ class ByteRenderer(out: OutputStream = new java.io.ByteArrayOutputStream(), inde
       matDepth: Int,
       ctx: Materializer.MaterializeContext)(implicit evaluator: EvalScope): Unit = {
     val keys =
-      if (ctx.sort) obj.visibleKeyNames.sorted(Util.CodepointStringOrdering)
+      if (ctx.sort) obj.sortedVisibleKeyNames
       else obj.visibleKeyNames
 
     openObjBrace()
diff --git a/sjsonnet/src/sjsonnet/Materializer.scala b/sjsonnet/src/sjsonnet/Materializer.scala
index 0742ca6e..d184a9e0 100644
--- a/sjsonnet/src/sjsonnet/Materializer.scala
+++ b/sjsonnet/src/sjsonnet/Materializer.scala
@@ -100,7 +100,7 @@ abstract class Materializer {
         else materializeInlineObj(obj, visitor, depth, ctx)
       } else {
         val keys =
-          if (ctx.sort) obj.visibleKeyNames.sorted(Util.CodepointStringOrdering)
+          if (ctx.sort) obj.sortedVisibleKeyNames
           else obj.visibleKeyNames
         val ov = visitor.visitObject(keys.length, jsonableKeys = true, -1)
         var i = 0
@@ -432,7 +432,7 @@ abstract class Materializer {
     storePos(obj.pos)
     obj.triggerAllAsserts(ctx.brokenAssertionLogic)
     val keyNames =
-      if (ctx.sort) obj.visibleKeyNames.sorted(Util.CodepointStringOrdering)
+      if (ctx.sort) obj.sortedVisibleKeyNames
       else obj.visibleKeyNames
     val objVisitor = visitor.visitObject(keyNames.length, jsonableKeys = true, -1)
     stack.push(
diff --git a/sjsonnet/src/sjsonnet/Val.scala b/sjsonnet/src/sjsonnet/Val.scala
index 4b5d7633..af4acbaa 100644
--- a/sjsonnet/src/sjsonnet/Val.scala
+++ b/sjsonnet/src/sjsonnet/Val.scala
@@ -884,7 +884,18 @@ object Val {
      * Cached sorted field order for inline objects. Shared across all objects from the same
      * MemberList to avoid per-object sort + allocation.
      */
-    @volatile private[sjsonnet] var _sortedInlineOrder: Array[Int] = null
+    private[sjsonnet] var _sortedInlineOrder: Array[Int] = null
+
+    private[sjsonnet] var _sortedVisibleKeyNames: Array[String] = null
+
+    private[sjsonnet] def sortedVisibleKeyNames: Array[String] = {
+      var r = _sortedVisibleKeyNames
+      if (r == null) {
+        r = visibleKeyNames.sorted(Util.CodepointStringOrdering)
+        _sortedVisibleKeyNames = r
+      }
+      r
+    }
 
     /**
      * When true, field caching can be skipped during materialization because no field body
@@ -1402,7 +1413,7 @@ object Val {
 
     def foreachElement(sort: Boolean, pos: Position)(f: (String, Val) => Unit)(implicit
         ev: EvalScope): Unit = {
-      val keys = if (sort) visibleKeyNames.sorted(Util.CodepointStringOrdering) else visibleKeyNames
+      val keys = if (sort) sortedVisibleKeyNames else visibleKeyNames
       for (k <- keys) {
         val v = value(k, pos)
         f(k, v)