diff --git a/src/App/GroupExtension.h b/src/App/GroupExtension.h
index 2da27c3a0..84b0b9c88 100644
--- a/src/App/GroupExtension.h
+++ b/src/App/GroupExtension.h
@@ -30,7 +30,6 @@
 #include "DocumentObjectExtension.h"
 #include <vector>
 
-
 namespace App
 {
 class DocumentObjectGroup;
diff --git a/src/Mod/PartDesign/Gui/Command.cpp b/src/Mod/PartDesign/Gui/Command.cpp
index 801b20165..5df71fc61 100644
--- a/src/Mod/PartDesign/Gui/Command.cpp
+++ b/src/Mod/PartDesign/Gui/Command.cpp
@@ -440,7 +440,9 @@ void CmdPartDesignNewSketch::activated(int iMsg)
         unsigned validPlanes = 0;
 
         auto group = App::GeoFeatureGroupExtension::getGroupOfObject ( pcActiveBody );
-        auto geoGroup = dynamic_cast<App::GeoFeatureGroupExtension*>(group->getExtension(App::GeoFeatureGroupExtension::getClassTypeId()));
+        App::GeoFeatureGroupExtension* geoGroup = nullptr;
+        if(group)
+            geoGroup = dynamic_cast<App::GeoFeatureGroupExtension*>(group->getExtension(App::GeoFeatureGroupExtension::getClassTypeId()));
 
         std::vector<App::DocumentObject*> planes;
         std::vector<PartDesignGui::TaskFeaturePick::featureStatus> status;
diff --git a/src/Mod/Test/Document.py b/src/Mod/Test/Document.py
index 98ebbd326..f2b4b3a18 100644
--- a/src/Mod/Test/Document.py
+++ b/src/Mod/Test/Document.py
@@ -188,15 +188,38 @@ class DocumentBasicCases(unittest.TestCase):
     grp = self.Doc.addObject("App::DocumentObject", "Extension_2")
     #we should have all methods we need to handle extensions 
     try:
-      self.failUnless(not grp.hasExtension("App::GroupExtension"))
-      grp.addExtension("App::GroupExtension", self)
+      self.failUnless(not grp.hasExtension("App::GroupExtensionPython"))
+      grp.addExtension("App::GroupExtensionPython", self)
+      self.failUnless(grp.hasExtension("App::GroupExtension"))
+      self.failUnless(grp.hasExtension("App::GroupExtensionPython"))
       grp.addObject(obj)
+      self.failUnless(len(grp.Group) == 1)
       self.failUnless(grp.Group[0] == obj)
     except:
       self.failUnless(True)
+      
+    #test if the method override works
+    class SpecialGroup():
+        def allowObject(self, obj):
+            return False;
     
-    self.Doc.remove(obj)
+    callback = SpecialGroup()
+    grp2 = self.Doc.addObject("App::DocumentObject", "Extension_3")  
+    grp2.addExtension("App::GroupExtensionPython", callback)
+    
+    try:
+      self.failUnless(grp2.hasExtension("App::GroupExtension"))
+      grp2.addObject(obj)
+      self.failUnless(len(grp2.Group) == 0)
+    except:
+      self.failUnless(True)
+    
+    self.Doc.removeObject(grp.Name)
+    self.Doc.removeObject(grp2.Name)
+    self.Doc.removeObject(obj.Name)
     del obj
+    del grp
+    del grp2
 
   def tearDown(self):
     #closing doc