diff --git a/src/zserio/service/rmi/RMIClient.java b/src/zserio/service/rmi/RMIClient.java
index dfe2501..28e471a 100644
--- a/src/zserio/service/rmi/RMIClient.java
+++ b/src/zserio/service/rmi/RMIClient.java
@@ -64,7 +64,7 @@ public RMIClient(String serviceFullName, String host, int port) throws RemoteExc
      * Implementation of ServiceClientInterface::callMethod.
      */
     @Override
-    public <T extends Writer> byte[] callMethod(String methodName, ServiceData<T> request, Object context)
+    public byte[] callMethod(String methodName, ServiceData<? extends Writer> request, Object context)
     {
         try
         {
diff --git a/src/zserio/service/rmi/RMIServer.java b/src/zserio/service/rmi/RMIServer.java
index 256eb98..09d6187 100644
--- a/src/zserio/service/rmi/RMIServer.java
+++ b/src/zserio/service/rmi/RMIServer.java
@@ -35,7 +35,7 @@ public RMIServer(ServiceInterface serviceImpl, String serviceFullName)
     @Override
     public byte[] callMethod(String methodName, byte[] requestData) throws RemoteException
     {
-        final ServiceData<?> serviceData = serviceImpl.callMethod(methodName, requestData, null);
+        final ServiceData<? extends Writer> serviceData = serviceImpl.callMethod(methodName, requestData, null);
         return serviceData.getByteArray();
     }