diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/jvm-common/infrastructure/Serializer.kt.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/jvm-common/infrastructure/Serializer.kt.mustache
index 24b95f65b32..57fe58a103f 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/jvm-common/infrastructure/Serializer.kt.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/jvm-common/infrastructure/Serializer.kt.mustache
@@ -143,6 +143,7 @@ import java.util.concurrent.atomic.AtomicLong
     val kotlinxSerializationJson: Json by lazy {
         Json {
             serializersModule = kotlinxSerializationAdapters
+            encodeDefaults = true
             ignoreUnknownKeys = true
             isLenient = true
         }
diff --git a/samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt b/samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
index 82473d228a0..951484b2180 100644
--- a/samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
+++ b/samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
@@ -45,6 +45,7 @@ object Serializer {
     val kotlinxSerializationJson: Json by lazy {
         Json {
             serializersModule = kotlinxSerializationAdapters
+            encodeDefaults = true
             ignoreUnknownKeys = true
             isLenient = true
         }
diff --git a/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt b/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
index 82473d228a0..951484b2180 100644
--- a/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
+++ b/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
@@ -45,6 +45,7 @@ object Serializer {
     val kotlinxSerializationJson: Json by lazy {
         Json {
             serializersModule = kotlinxSerializationAdapters
+            encodeDefaults = true
             ignoreUnknownKeys = true
             isLenient = true
         }
diff --git a/samples/client/petstore/kotlin-uppercase-enum/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt b/samples/client/petstore/kotlin-uppercase-enum/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
index 82473d228a0..951484b2180 100644
--- a/samples/client/petstore/kotlin-uppercase-enum/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
+++ b/samples/client/petstore/kotlin-uppercase-enum/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt
@@ -45,6 +45,7 @@ object Serializer {
     val kotlinxSerializationJson: Json by lazy {
         Json {
             serializersModule = kotlinxSerializationAdapters
+            encodeDefaults = true
             ignoreUnknownKeys = true
             isLenient = true
         }