diff --git a/extensions/resteasy-reactive/quarkus-resteasy-reactive-kotlin-serialization/runtime/src/main/kotlin/io/quarkus/kotlin/serialization/KotlinSerializationMessageBodyWriter.kt b/extensions/resteasy-reactive/quarkus-resteasy-reactive-kotlin-serialization/runtime/src/main/kotlin/io/quarkus/kotlin/serialization/KotlinSerializationMessageBodyWriter.kt
index 134e5592e7ad6..866c528c7a4e3 100644
--- a/extensions/resteasy-reactive/quarkus-resteasy-reactive-kotlin-serialization/runtime/src/main/kotlin/io/quarkus/kotlin/serialization/KotlinSerializationMessageBodyWriter.kt
+++ b/extensions/resteasy-reactive/quarkus-resteasy-reactive-kotlin-serialization/runtime/src/main/kotlin/io/quarkus/kotlin/serialization/KotlinSerializationMessageBodyWriter.kt
@@ -30,7 +30,7 @@ class KotlinSerializationMessageBodyWriter(private val json: Json) : AllWriteabl
         if (o is String) { // YUK: done in order to avoid adding extra quotes...
             entityStream.write(o.toByteArray(StandardCharsets.UTF_8))
         } else {
-            json.encodeToStream(serializer(o.javaClass), o, entityStream)
+            json.encodeToStream(serializer(genericType), o, entityStream)
         }
     }
 
diff --git a/integration-tests/resteasy-reactive-kotlin/standard/src/main/kotlin/io/quarkus/it/resteasy/reactive/kotlin/Filters.kt b/integration-tests/resteasy-reactive-kotlin/standard/src/main/kotlin/io/quarkus/it/resteasy/reactive/kotlin/Filters.kt
index 436cf2fb4a240..1a20619ff2f15 100644
--- a/integration-tests/resteasy-reactive-kotlin/standard/src/main/kotlin/io/quarkus/it/resteasy/reactive/kotlin/Filters.kt
+++ b/integration-tests/resteasy-reactive-kotlin/standard/src/main/kotlin/io/quarkus/it/resteasy/reactive/kotlin/Filters.kt
@@ -7,6 +7,7 @@ import org.jboss.resteasy.reactive.server.SimpleResourceInfo
 import java.security.SecureRandom
 import javax.ws.rs.container.ContainerRequestContext
 import javax.ws.rs.container.ContainerResponseContext
+import javax.ws.rs.container.ResourceInfo
 import javax.ws.rs.core.Response
 import javax.ws.rs.core.UriInfo
 
@@ -33,9 +34,10 @@ class Filters {
     }
 
     @ServerResponseFilter
-    suspend fun addResponseHeader(context: ContainerResponseContext, simpleResourceInfo: SimpleResourceInfo) {
+    suspend fun addResponseHeader(context: ContainerResponseContext, simpleResourceInfo: SimpleResourceInfo, resourceInfo: ResourceInfo) {
         delay(100)
         context.headers.add("method", simpleResourceInfo.methodName)
+        context.headers.add("method2", resourceInfo.resourceMethod.name)
         delay(100)
     }
 }