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 28650279d1830..c74c5f3b24d26 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
@@ -27,7 +27,7 @@ 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(o, entityStream)
+            json.encodeToStream(serializer(o.javaClass) , o, entityStream)
         }
     }
 
diff --git a/integration-tests/kotlin-serialization/src/main/kotlin/io/quarkus/it/kotser/GreetingResource.kt b/integration-tests/kotlin-serialization/src/main/kotlin/io/quarkus/it/kotser/GreetingResource.kt
index aa79185c7e35e..c3eddcab2088d 100644
--- a/integration-tests/kotlin-serialization/src/main/kotlin/io/quarkus/it/kotser/GreetingResource.kt
+++ b/integration-tests/kotlin-serialization/src/main/kotlin/io/quarkus/it/kotser/GreetingResource.kt
@@ -2,6 +2,7 @@ package io.quarkus.it.kotser
 
 import io.quarkus.it.kotser.model.Person
 import io.quarkus.runtime.annotations.RegisterForReflection
+import kotlinx.coroutines.flow.flowOf
 import java.lang.reflect.Method
 import javax.ws.rs.Consumes
 import javax.ws.rs.GET
@@ -15,6 +16,10 @@ import kotlin.reflect.jvm.javaMethod
 @Path("/")
 @RegisterForReflection
 class GreetingResource {
+    @Path("flow")
+    @GET
+    @Produces(MediaType.APPLICATION_JSON)
+    fun flowHello() = flowOf(Person("Jim Halpert"))
 
     @GET
     @Produces(MediaType.APPLICATION_JSON)
diff --git a/integration-tests/kotlin-serialization/src/main/resources/application.properties b/integration-tests/kotlin-serialization/src/main/resources/application.properties
index 86df10fe75526..4dadb74e15205 100644
--- a/integration-tests/kotlin-serialization/src/main/resources/application.properties
+++ b/integration-tests/kotlin-serialization/src/main/resources/application.properties
@@ -1,3 +1 @@
-quarkus.kotlin-serialization.json.encode-defaults=true
-quarkus.kotlin-serialization.json.pretty-print=true
-quarkus.kotlin-serialization.json.pretty-print-indent=\ \ 
\ No newline at end of file
+quarkus.kotlin-serialization.json.encode-defaults=true
\ No newline at end of file
diff --git a/integration-tests/kotlin-serialization/src/test/kotlin/io/quarkus/it/kotser/ResourceTest.kt b/integration-tests/kotlin-serialization/src/test/kotlin/io/quarkus/it/kotser/ResourceTest.kt
index 3ba3015b9b402..5054b2afbe8af 100644
--- a/integration-tests/kotlin-serialization/src/test/kotlin/io/quarkus/it/kotser/ResourceTest.kt
+++ b/integration-tests/kotlin-serialization/src/test/kotlin/io/quarkus/it/kotser/ResourceTest.kt
@@ -12,20 +12,24 @@ import javax.ws.rs.core.MediaType
 
 @QuarkusTest
 open class ResourceTest {
+    @Test
+    fun testGetFlow() {
+        When {
+            get("/flow")
+        } Then {
+            statusCode(200)
+            body(`is`("""[{"name":"Jim Halpert","defaulted":"hi there!"}]"""))
+        }
+    }
+
     @Test
     fun testGet() {
-         When {
-             get("/")
-         } Then {
-             statusCode(200)
-             body(`is`(
-                 """
-                    {
-                      "name": "Jim Halpert",
-                      "defaulted": "hi there!"
-                    }""".trimIndent()
-             ))
-         }
+        When {
+            get("/")
+        } Then {
+            statusCode(200)
+            body(`is`("""{"name":"Jim Halpert","defaulted":"hi there!"}"""))
+        }
     }
 
     @Test
@@ -34,13 +38,7 @@ open class ResourceTest {
             get("/suspend")
         } Then {
             statusCode(200)
-            body(`is`(
-                """
-                    {
-                      "name": "Jim Halpert",
-                      "defaulted": "hi there!"
-                    }""".trimIndent()
-            ))
+            body(`is`("""{"name":"Jim Halpert","defaulted":"hi there!"}"""))
         }
     }
 
@@ -50,15 +48,7 @@ open class ResourceTest {
             get("/suspendList")
         } Then {
             statusCode(200)
-            body(`is`(
-                """
-[
-  {
-    "name": "Jim Halpert",
-    "defaulted": "hi there!"
-  }
-]
-""".trimIndent()))
+            body(`is`("""[{"name":"Jim Halpert","defaulted":"hi there!"}]"""))
         }
     }
 
@@ -71,11 +61,7 @@ open class ResourceTest {
             post("/")
         } Then {
             statusCode(200)
-            body(`is`("""
-                {
-                  "name": "Pam Halpert",
-                  "defaulted": "hi there!"
-                }""".trimIndent()))
+            body(`is`("""{"name":"Pam Halpert","defaulted":"hi there!"}"""))
         }
     }