diff --git a/fluent-kafka-streams-tests/src/main/java/com/bakdata/fluent_kafka_streams_tests/TestTopology.java b/fluent-kafka-streams-tests/src/main/java/com/bakdata/fluent_kafka_streams_tests/TestTopology.java
index 2af58f2..d1ff091 100644
--- a/fluent-kafka-streams-tests/src/main/java/com/bakdata/fluent_kafka_streams_tests/TestTopology.java
+++ b/fluent-kafka-streams-tests/src/main/java/com/bakdata/fluent_kafka_streams_tests/TestTopology.java
@@ -322,14 +322,16 @@ protected <K, V> TestTopology<K, V> with(
      * Get the default serde of the key type in your application.
      */
     private Serde<DefaultK> getDefaultKeySerde() {
-        return this.defaultKeySerde != null ? this.defaultKeySerde : this.getStreamsConfig().defaultKeySerde();
+        return this.defaultKeySerde != null ? this.defaultKeySerde
+                : (Serde<DefaultK>) this.getStreamsConfig().defaultKeySerde();
     }
 
     /**
      * Get the default serde of the value type in your application.
      */
     private Serde<DefaultV> getDefaultValueSerde() {
-        return this.defaultValueSerde != null ? this.defaultValueSerde : this.getStreamsConfig().defaultValueSerde();
+        return this.defaultValueSerde != null ? this.defaultValueSerde
+                : (Serde<DefaultV>) this.getStreamsConfig().defaultValueSerde();
     }
 
     /**