diff --git a/modules/openapi-generator/src/main/resources/kotlin-server/typeInfoAnnotation.mustache b/modules/openapi-generator/src/main/resources/kotlin-server/typeInfoAnnotation.mustache
index 88fddd2d51cb..ebe8826b0edb 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-server/typeInfoAnnotation.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-server/typeInfoAnnotation.mustache
@@ -1,4 +1,4 @@
-@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = {{#vendorExtensions.x-discriminator-visible-true}}true{{/vendorExtensions.x-discriminator-visible-true}}{{^vendorExtensions.x-discriminator-visible-true}}false{{/vendorExtensions.x-discriminator-visible-true}})
+@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = true)
 @com.fasterxml.jackson.annotation.JsonSubTypes(
 {{#discriminator.mappedModels}}
     com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = {{modelName}}::class, name = "{{^vendorExtensions.x-discriminator-value}}{{mappingName}}{{/vendorExtensions.x-discriminator-value}}{{#vendorExtensions.x-discriminator-value}}{{{vendorExtensions.x-discriminator-value}}}{{/vendorExtensions.x-discriminator-value}}"){{^-last}},{{/-last}}
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinServerCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinServerCodegenTest.java
index f931f659b431..1cea927f1de3 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinServerCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinServerCodegenTest.java
@@ -405,10 +405,17 @@ public void oneOfWithDiscriminator_generatesSealedClassWithDiscriminatorProperty
                 "sealed class Pet(",
                 "open val petType: kotlin.String",
                 "@com.fasterxml.jackson.annotation.JsonTypeInfo",
+                // every mapped child model declares/inherits the discriminator property, so
+                // Jackson must reuse it instead of injecting a second copy (duplicated key)
+                "include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY",
                 "property = \"petType\"",
                 "visible = true",
                 "@com.fasterxml.jackson.annotation.JsonSubTypes"
         );
+        assertFileNotContains(
+                petModel,
+                "include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY,"
+        );
     }
 
     @Test
@@ -571,12 +578,15 @@ public void fixJacksonJsonTypeInfoInheritance_canBeDisabled() throws IOException
         String outputPath = output.getAbsolutePath() + "/src/main/kotlin/org/openapitools/server";
         Path petModel = Paths.get(outputPath + "/models/Pet.kt");
 
-        // When fixJacksonJsonTypeInfoInheritance is false and parent has no properties,
-        // visible should be false for oneOf pattern
+        // With As.EXISTING_PROPERTY the discriminator is read from/written to the real
+        // property, which every mapped child model declares or inherits; visible=true
+        // keeps that property populated on deserialization so round-trips preserve it
         assertFileContains(
                 petModel,
-                "visible = false"
+                "include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY",
+                "visible = true"
         );
+        assertFileNotContains(petModel, "visible = false");
     }
 
     // ==================== useTags for JAXRS-SPEC ====================
diff --git a/samples/server/others/kotlin-server/polymorphism-allof-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt b/samples/server/others/kotlin-server/polymorphism-allof-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt
index 5812ac1944eb..b50931bae500 100644
--- a/samples/server/others/kotlin-server/polymorphism-allof-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt
+++ b/samples/server/others/kotlin-server/polymorphism-allof-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt
@@ -17,7 +17,7 @@ package org.openapitools.server.models
  * @param name 
  * @param petType 
  */
-@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY, property = "petType", visible = true)
+@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY, property = "petType", visible = true)
 @com.fasterxml.jackson.annotation.JsonSubTypes(
     com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Cat::class, name = "Cat"),
     com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Dog::class, name = "Dog")
diff --git a/samples/server/others/kotlin-server/polymorphism-and-discriminator-disabled-jackson-fix/src/main/kotlin/org/openapitools/server/models/Pet.kt b/samples/server/others/kotlin-server/polymorphism-and-discriminator-disabled-jackson-fix/src/main/kotlin/org/openapitools/server/models/Pet.kt
index 737a74aefcfb..9f0d58eacfe8 100644
--- a/samples/server/others/kotlin-server/polymorphism-and-discriminator-disabled-jackson-fix/src/main/kotlin/org/openapitools/server/models/Pet.kt
+++ b/samples/server/others/kotlin-server/polymorphism-and-discriminator-disabled-jackson-fix/src/main/kotlin/org/openapitools/server/models/Pet.kt
@@ -17,7 +17,7 @@ import org.openapitools.server.models.Dog
 /**
  * A pet
  */
-@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY, property = "petType", visible = false)
+@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY, property = "petType", visible = true)
 @com.fasterxml.jackson.annotation.JsonSubTypes(
     com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Cat::class, name = "cat"),
     com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Dog::class, name = "dog")
diff --git a/samples/server/others/kotlin-server/polymorphism-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt b/samples/server/others/kotlin-server/polymorphism-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt
index 30ada8deb372..191021901fee 100644
--- a/samples/server/others/kotlin-server/polymorphism-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt
+++ b/samples/server/others/kotlin-server/polymorphism-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt
@@ -18,7 +18,7 @@ import org.openapitools.server.models.Dog
  * A pet
  * @param petType 
  */
-@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY, property = "petType", visible = true)
+@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY, property = "petType", visible = true)
 @com.fasterxml.jackson.annotation.JsonSubTypes(
     com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Cat::class, name = "cat"),
     com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Dog::class, name = "dog")