diff --git a/src/App/ExtensionContainerPyImp.cpp b/src/App/ExtensionContainerPyImp.cpp
index 2dc70cd7cb..e09f4b3a56 100644
--- a/src/App/ExtensionContainerPyImp.cpp
+++ b/src/App/ExtensionContainerPyImp.cpp
@@ -198,9 +198,15 @@ PyObject* ExtensionContainerPy::hasExtension(PyObject *args) {
 PyObject* ExtensionContainerPy::addExtension(PyObject *args) {
 
     char *typeId;
-    if (!PyArg_ParseTuple(args, "s", &typeId))
+    PyObject* proxy = nullptr;
+    if (!PyArg_ParseTuple(args, "s|O", &typeId, &proxy))
         return NULL;
 
+    if (proxy) {
+        PyErr_SetString(PyExc_DeprecationWarning, "A proxy object as seconbd argument is not needed any more. Please adjust your code");
+        PyErr_Print();
+    }
+
     //get the extension type asked for
     Base::Type extension =  Base::Type::fromName(typeId);
     if (extension.isBad() || !extension.isDerivedFrom(App::Extension::getExtensionClassTypeId())) {