diff --git a/src/App/Extension.cpp b/src/App/Extension.cpp
index 0a150a9b40..c8e8af584f 100644
--- a/src/App/Extension.cpp
+++ b/src/App/Extension.cpp
@@ -69,6 +69,7 @@ using namespace App;
 Extension::~Extension()
 {
     if (!ExtensionPythonObject.is(Py::_None())) {
+        Base::PyGILStateLocker lock;
         // Remark: The API of Py::Object has been changed to set whether the wrapper owns the passed
         // Python object or not. In the constructor we forced the wrapper to own the object so we
         // need not to dec'ref the Python object any more. But we must still invalidate the Python
diff --git a/src/App/Extension.pyi b/src/App/Extension.pyi
index 2246d43946..0005862c31 100644
--- a/src/App/Extension.pyi
+++ b/src/App/Extension.pyi
@@ -1,3 +1,4 @@
+from typing import Final, Any
 from Base.PyObjectBase import PyObjectBase
 
 
@@ -7,4 +8,6 @@ class Extension(PyObjectBase):
     Author: Stefan Troeger (stefantroeger@gmx.net)
     Licence: LGPL
     """
-    ...
+
+    ExtendedObject: Final[Any] = None
+    """Get extended container object"""
diff --git a/src/App/ExtensionPyImp.cpp b/src/App/ExtensionPyImp.cpp
index 23a1cf2b74..4b8afc4123 100644
--- a/src/App/ExtensionPyImp.cpp
+++ b/src/App/ExtensionPyImp.cpp
@@ -23,9 +23,9 @@
 
 #include "PreCompiled.h"
 
-#include "Application.h"
+#include "ExtensionContainer.h"
 
-// inclusion of the generated files (generated out of PropertyContainerPy.xml)
+// inclusion of the generated files (generated out of ExtensionPy.pyi)
 #include <App/ExtensionPy.h>
 #include <App/ExtensionPy.cpp>
 
@@ -37,6 +37,11 @@ std::string ExtensionPy::representation() const
     return {"<extension>"};
 }
 
+Py::Object ExtensionPy::getExtendedObject() const
+{
+    return Py::Object(getExtensionPtr()->getExtendedContainer()->getPyObject(), true);
+}
+
 PyObject* ExtensionPy::getCustomAttributes(const char* /*attr*/) const
 {
     return nullptr;
diff --git a/src/App/ExtensionPython.h b/src/App/ExtensionPython.h
index a4d8e7428b..52c4ed3db4 100644
--- a/src/App/ExtensionPython.h
+++ b/src/App/ExtensionPython.h
@@ -63,12 +63,12 @@ using ExtensionPython = ExtensionPythonT<App::Extension>;
     Base::PyGILStateLocker lock;                                                                   \
     Py::Object result;                                                                             \
     try {                                                                                          \
-        Property* proxy = this->getExtendedContainer()->getPropertyByName("Proxy");                \
-        if (proxy && proxy->is<PropertyPythonObject>()) {                                          \
-            Py::Object feature = static_cast<PropertyPythonObject*>(proxy)->getValue();            \
-            if (feature.hasAttr(std::string("function"))) {                                        \
+        App::Property* proxy = this->getExtendedContainer()->getPropertyByName("Proxy");           \
+        if (proxy && proxy->is<App::PropertyPythonObject>()) {                                     \
+            Py::Object feature = static_cast<App::PropertyPythonObject*>(proxy)->getValue();       \
+            if (feature.hasAttr(std::string(#function))) {                                         \
                 if (feature.hasAttr("__object__")) {                                               \
-                    Py::Callable method(feature.getAttr(std::string("function")));
+                    Py::Callable method(feature.getAttr(std::string(#function)));
 
 
 #define EXTENSION_PROXY_SECOND(function)                                                           \
@@ -76,7 +76,7 @@ using ExtensionPython = ExtensionPythonT<App::Extension>;
     }                                                                                              \
     else                                                                                           \
     {                                                                                              \
-        Py::Callable method(feature.getAttr(std::string("function")));
+        Py::Callable method(feature.getAttr(std::string(#function)));
 
 #define EXTENSION_PROXY_THIRD()                                                                    \
     result = method.apply(args);                                                                   \
@@ -109,13 +109,13 @@ using ExtensionPython = ExtensionPythonT<App::Extension>;
     EXTENSION_PROXY_THIRD()
 
 #define EXTENSION_PYTHON_OVERRIDE_VOID_NOARGS(function)                                            \
-    virtual void function() override { EXTENSION_PROXY_NOARGS(function) };
+    virtual void function() override { EXTENSION_PROXY_NOARG(function) };
 
 #define EXTENSION_PYTHON_OVERRIDE_OBJECT_NOARGS(function)                                          \
     virtual PyObject* function() override                                                          \
     {                                                                                              \
-        EXTENSION_PROXY_NOARGS(function)                                                           \
-        return res.ptr();                                                                          \
+        EXTENSION_PROXY_NOARG(function)                                                            \
+        return result.ptr();                                                                       \
     };
 
 }  // namespace App
diff --git a/src/Mod/Test/Document.py b/src/Mod/Test/Document.py
index efc93c62ee..75d207dcbb 100644
--- a/src/Mod/Test/Document.py
+++ b/src/Mod/Test/Document.py
@@ -431,7 +431,7 @@ class DocumentBasicCases(unittest.TestCase):
 
         # test if the method override works
         class SpecialGroup:
-            def allowObject(self, obj):
+            def allowObject(self, ext, obj):
                 return False
 
         callback = SpecialGroup()
@@ -444,7 +444,7 @@ class DocumentBasicCases(unittest.TestCase):
             grp2.addObject(obj)
             self.assertTrue(len(grp2.Group) == 0)
         except Exception:
-            self.assertTrue(True)
+            self.assertTrue(False)
 
         self.Doc.removeObject(grp.Name)
         self.Doc.removeObject(grp2.Name)
@@ -721,7 +721,7 @@ class SaveRestoreSpecialGroup:
         obj.addExtension("App::GroupExtensionPython")
         obj.Proxy = self
 
-    def allowObject(self, obj):
+    def allowObject(self, ext, obj):
         return False