diff --git a/src/App/FeaturePythonPyImp.inl b/src/App/FeaturePythonPyImp.inl
index e280a13ba7..af076e56a3 100644
--- a/src/App/FeaturePythonPyImp.inl
+++ b/src/App/FeaturePythonPyImp.inl
@@ -330,13 +330,16 @@ PyObject*  FeaturePythonPyT<FeaturePyT>::addProperty(PyObject *args)
 {
     char *sType,*sName=0,*sGroup=0,*sDoc=0;
     short attr=0;
+    std::string sDocStr;
     PyObject *ro = Py_False, *hd = Py_False;
     if (!PyArg_ParseTuple(args, "s|ssethO!O!", &sType,&sName,&sGroup,"utf-8",&sDoc,&attr,
         &PyBool_Type, &ro, &PyBool_Type, &hd))     // convert args: Python->C
         return NULL;                             // NULL triggers exception 
 
-    std::string sDocStr = std::string(sDoc);
-    PyMem_Free(sDoc);
+    if (sDoc) {
+        sDocStr = sDoc;
+        PyMem_Free(sDoc);
+    }
 
     Property* prop=0;
     prop = FeaturePyT::getDocumentObjectPtr()->addDynamicProperty(sType,sName,sGroup,sDocStr.c_str(),attr,
diff --git a/src/Gui/ViewProviderPythonFeaturePyImp.cpp b/src/Gui/ViewProviderPythonFeaturePyImp.cpp
index d8697ae294..2bbbdbbc45 100644
--- a/src/Gui/ViewProviderPythonFeaturePyImp.cpp
+++ b/src/Gui/ViewProviderPythonFeaturePyImp.cpp
@@ -67,13 +67,16 @@ PyObject*  ViewProviderPythonFeaturePy::addProperty(PyObject *args)
 {
     char *sType,*sName=0,*sGroup=0,*sDoc=0;
     short attr=0;
+    std::string sDocStr;
     PyObject *ro = Py_False, *hd = Py_False;
     if (!PyArg_ParseTuple(args, "s|ssethO!O!", &sType,&sName,&sGroup,"utf-8",&sDoc,&attr,
         &PyBool_Type, &ro, &PyBool_Type, &hd))     // convert args: Python->C
         return NULL;                             // NULL triggers exception 
 
-    std::string sDocStr = std::string(sDoc);
-    PyMem_Free(sDoc);
+    if (sDoc) {
+        sDocStr = sDoc;
+        PyMem_Free(sDoc);
+    }
 
     App::Property* prop=0;
     prop = getViewProviderPythonFeaturePtr()->addDynamicProperty(sType,sName,sGroup,sDocStr.c_str(),attr,