diff --git a/sdk-common/src/main/java/dev/restate/sdk/common/CoreSerdes.java b/sdk-common/src/main/java/dev/restate/sdk/common/CoreSerdes.java
index 67241029..6158ec0d 100644
--- a/sdk-common/src/main/java/dev/restate/sdk/common/CoreSerdes.java
+++ b/sdk-common/src/main/java/dev/restate/sdk/common/CoreSerdes.java
@@ -171,6 +171,11 @@ public T deserialize(byte[] value) {
           throw new RuntimeException("Cannot create JsonGenerator", e);
         }
       }
+
+      @Override
+      public String contentType() {
+        return "application/json";
+      }
     };
   }
 }