diff --git a/src/Mod/Part/App/GeometryPyImp.cpp b/src/Mod/Part/App/GeometryPyImp.cpp
index 7d89f9a13b..4f0fffe730 100644
--- a/src/Mod/Part/App/GeometryPyImp.cpp
+++ b/src/Mod/Part/App/GeometryPyImp.cpp
@@ -261,6 +261,10 @@ PyObject* GeometryPy::getExtensionOfType(PyObject *args)
                 PyErr_SetString(PartExceptionOCCError, "Geometry extension does not exist anymore.");
                 return 0;
             }
+            catch(Base::NotImplementedError) {
+                PyErr_SetString(Part::PartExceptionOCCError, "Geometry extension does not implement a Python counterpart.");
+                return 0;
+            }
         }
         else
         {
@@ -296,6 +300,10 @@ PyObject* GeometryPy::getExtensionOfName(PyObject *args)
             PyErr_SetString(PartExceptionOCCError, "Geometry extension does not exist anymore.");
             return 0;
         }
+        catch(Base::NotImplementedError) {
+            PyErr_SetString(Part::PartExceptionOCCError, "Geometry extension does not implement a Python counterpart.");
+            return 0;
+        }
 
     }
 
@@ -408,7 +416,7 @@ PyObject* GeometryPy::getExtensions(PyObject *args)
     try {
         const std::vector<std::weak_ptr<const GeometryExtension>> ext = this->getGeometryPtr()->getExtensions();
 
-        PyObject* list = PyList_New(ext.size());
+        PyObject* list = PyList_New(0);
 
         for (std::size_t i=0; i<ext.size(); ++i) {
 
@@ -417,10 +425,17 @@ PyObject* GeometryPy::getExtensions(PyObject *args)
 
             if(p) {
                 // we create a python copy and add it to the list
-                Py::Tuple tuple;
-                PyObject* cpy = static_cast<GeometryExtensionPy *>(p->getPyObject())->copy(tuple.ptr());
 
-                PyList_SetItem( list, i, cpy);
+                try {
+                    Py::Tuple tuple;
+                    PyObject* cpy = static_cast<GeometryExtensionPy *>(p->getPyObject())->copy(tuple.ptr());
+
+                    PyList_Append( list, cpy);
+                    Py_DECREF(cpy);
+                }
+                catch(Base::NotImplementedError) {
+                    // silently ignoring extensions not having a Python object
+                }
             }
         }
 
diff --git a/src/Mod/Sketcher/App/ExternalGeometryFacade.h b/src/Mod/Sketcher/App/ExternalGeometryFacade.h
index eed4591e8f..788ffbcb0b 100644
--- a/src/Mod/Sketcher/App/ExternalGeometryFacade.h
+++ b/src/Mod/Sketcher/App/ExternalGeometryFacade.h
@@ -41,6 +41,10 @@ class ExternalGeometryFacadePy;
 //
 // Exactly the same considerations as for GeometryFacade apply (see documentation of GeometryFacade).
 //
+// It was not made publicly deriving from GeometryFacade because it is not possible to differentiate functions by return type, which is the
+// case of getFacade() returning a unique_ptr to GeometryFacade in GeometryFacade, and one to ExternalGeometryFacade. I have not managed to
+// find a good solution to this problem, thus the code duplication.
+//
 // Summary Remarks:
 // It is intended to have a separate type (not being a Geometry type).
 // it is intended to have the relevant interface in full for the sketcher extension only
diff --git a/src/Mod/Sketcher/App/ExternalGeometryFacadePyImp.cpp b/src/Mod/Sketcher/App/ExternalGeometryFacadePyImp.cpp
index 50b29dcdb7..57bc771906 100644
--- a/src/Mod/Sketcher/App/ExternalGeometryFacadePyImp.cpp
+++ b/src/Mod/Sketcher/App/ExternalGeometryFacadePyImp.cpp
@@ -318,6 +318,10 @@ PyObject* ExternalGeometryFacadePy::getExtensionOfType(PyObject *args)
                 PyErr_SetString(Part::PartExceptionOCCError, "Geometry extension does not exist anymore.");
                 return 0;
             }
+            catch(Base::NotImplementedError) {
+                PyErr_SetString(Part::PartExceptionOCCError, "Geometry extension does not implement a Python counterpart.");
+                return 0;
+            }
         }
         else
         {
@@ -353,6 +357,10 @@ PyObject* ExternalGeometryFacadePy::getExtensionOfName(PyObject *args)
             PyErr_SetString(Part::PartExceptionOCCError, "Geometry extension does not exist anymore.");
             return 0;
         }
+        catch(Base::NotImplementedError) {
+            PyErr_SetString(Part::PartExceptionOCCError, "Geometry extension does not implement a Python counterpart.");
+            return 0;
+        }
 
     }
 
@@ -465,7 +473,7 @@ PyObject* ExternalGeometryFacadePy::getExtensions(PyObject *args)
     try {
         const std::vector<std::weak_ptr<const Part::GeometryExtension>> ext = this->getExternalGeometryFacadePtr()->getExtensions();
 
-        PyObject* list = PyList_New(ext.size());
+        PyObject* list = PyList_New(0);
 
         for (std::size_t i=0; i<ext.size(); ++i) {
 
@@ -473,10 +481,16 @@ PyObject* ExternalGeometryFacadePy::getExtensions(PyObject *args)
 
             if(p) {
                 // we create a python copy and add it to the list
-                Py::Tuple tuple;
-                PyObject* cpy = static_cast<Part::GeometryExtensionPy *>(std::const_pointer_cast<Part::GeometryExtension>(p)->getPyObject())->copy(tuple.ptr());
+                try {
+                    Py::Tuple tuple;
+                    PyObject* cpy = static_cast<Part::GeometryExtensionPy *>(std::const_pointer_cast<Part::GeometryExtension>(p)->getPyObject())->copy(tuple.ptr());
 
-                PyList_SetItem( list, i, cpy);
+                    PyList_Append( list, cpy);
+                    Py_DECREF(cpy);
+                }
+                catch(Base::NotImplementedError) {
+                    // silently ignoring extensions not having a Python object
+                }
             }
         }
 
diff --git a/src/Mod/Sketcher/App/GeometryFacadePyImp.cpp b/src/Mod/Sketcher/App/GeometryFacadePyImp.cpp
index 1c5d4f8a16..7ea43e12ad 100644
--- a/src/Mod/Sketcher/App/GeometryFacadePyImp.cpp
+++ b/src/Mod/Sketcher/App/GeometryFacadePyImp.cpp
@@ -297,6 +297,10 @@ PyObject* GeometryFacadePy::getExtensionOfType(PyObject *args)
                 PyErr_SetString(Part::PartExceptionOCCError, "Geometry extension does not exist anymore.");
                 return 0;
             }
+            catch(Base::NotImplementedError) {
+                PyErr_SetString(Part::PartExceptionOCCError, "Geometry extension does not implement a Python counterpart.");
+                return 0;
+            }
         }
         else
         {
@@ -332,7 +336,10 @@ PyObject* GeometryFacadePy::getExtensionOfName(PyObject *args)
             PyErr_SetString(Part::PartExceptionOCCError, "Geometry extension does not exist anymore.");
             return 0;
         }
-
+        catch(Base::NotImplementedError) {
+            PyErr_SetString(Part::PartExceptionOCCError, "Geometry extension does not implement a Python counterpart.");
+            return 0;
+        }
     }
 
     PyErr_SetString(Part::PartExceptionOCCError, "A string with the name of the geometry extension was expected");
@@ -444,7 +451,7 @@ PyObject* GeometryFacadePy::getExtensions(PyObject *args)
     try {
         const std::vector<std::weak_ptr<const Part::GeometryExtension>> ext = this->getGeometryFacadePtr()->getExtensions();
 
-        PyObject* list = PyList_New(ext.size());
+        PyObject* list = PyList_New(0);
 
         for (std::size_t i=0; i<ext.size(); ++i) {
 
@@ -453,9 +460,16 @@ PyObject* GeometryFacadePy::getExtensions(PyObject *args)
             if(p) {
                 // we create a python copy and add it to the list
                 Py::Tuple tuple;
-                PyObject* cpy = static_cast<Part::GeometryExtensionPy *>(std::const_pointer_cast<Part::GeometryExtension>(p)->getPyObject())->copy(tuple.ptr());
 
-                PyList_SetItem( list, i, cpy);
+                try {
+                    PyObject* cpy = static_cast<Part::GeometryExtensionPy *>(std::const_pointer_cast<Part::GeometryExtension>(p)->getPyObject())->copy(tuple.ptr());
+
+                    PyList_Append( list, cpy);
+                    Py_DECREF(cpy);
+                }
+                catch(Base::NotImplementedError) {
+                    // silently ignoring extensions not having a Python object
+                }
             }
         }