diff --git a/src/clntdata.sip b/src/clntdata.sip
index 09a6c8ad..c5cd239f 100644
--- a/src/clntdata.sip
+++ b/src/clntdata.sip
@@ -11,29 +11,15 @@
 
 
 %ModuleHeaderCode
-    // A wxClientData that holds a reference to a Python object
-    class wxPyClientData : public wxClientData 
-    {
-    public:
-        wxPyClientData(PyObject* obj, bool incref=true) 
-        {
-            m_obj = obj;
-            m_incRef = incref;
-            if (incref) {
-                wxPyBLOCK_THREADS( Py_INCREF(m_obj) );
-                }
-        }
-        ~wxPyClientData() 
-        {
-            if (m_incRef) {
-                wxPyBLOCK_THREADS( Py_DECREF(m_obj) );
-            }
-            m_obj = NULL;
-        }
-        PyObject* m_obj;
-        bool      m_incRef;
-    };
- 
+// A wxClientData that holds a reference to a Python object
+class wxPyClientData : public wxPyUserDataHelper<wxClientData>
+{
+public:
+    wxPyClientData(PyObject* obj = NULL)
+        : wxPyUserDataHelper<wxClientData>(obj)
+    { }
+};
+
 %End
 
 
@@ -59,13 +45,7 @@
     %ConvertFromTypeCode
         // Code to convert a wxClientData back to the PyObject.
         PyObject* obj;
-        if (sipCpp == NULL) {
-            obj = Py_None;
-        } else {            
-            wxPyClientData* data = static_cast<wxPyClientData*>(sipCpp);  // TODO: verify poitner type?
-            obj = data->m_obj;
-        }
-        Py_INCREF(obj);
+        obj = wxPyClientData::SafeGetData(static_cast<wxPyClientData*>(sipCpp));
         return obj;
     %End
     
diff --git a/src/treeitemdata.sip b/src/treeitemdata.sip
index b31fed8c..6f4e213f 100644
--- a/src/treeitemdata.sip
+++ b/src/treeitemdata.sip
@@ -15,21 +15,14 @@
 #include <wx/treebase.h>
 
 // A wxTreeItemData that knows what to do with PyObjects for maintianing the refcount
-class wxPyTreeItemData : public wxTreeItemData {
+class wxPyTreeItemData : public wxPyUserDataHelper<wxTreeItemData>
+{
 public:
-    wxPyTreeItemData(PyObject* obj = NULL) {
-        if (obj == NULL)
-            obj = Py_None;
-        wxPyBLOCK_THREADS( Py_INCREF(obj) );
-        m_obj = obj;
-    }
+    wxPyTreeItemData(PyObject* obj = NULL)
+        : wxPyUserDataHelper<wxTreeItemData>(obj)
+    { }
+};
 
-    ~wxPyTreeItemData() {
-        wxPyBLOCK_THREADS( Py_DECREF(m_obj) );
-    }
-
-    PyObject* m_obj;
-};    
 %End
 
 
@@ -41,7 +34,7 @@ public:
             return TRUE; // any python object is valid
         }
         
-        // Code to create a new wxClientData from the PyObject
+        // Code to create a new wxTreeItemData from the PyObject
         wxPyTreeItemData* data =  new wxPyTreeItemData(sipPy);
         *sipCppPtr = data;
         return sipGetState(sipTransferObj);
@@ -51,13 +44,7 @@ public:
     %ConvertFromTypeCode
         // Code to convert a wxPyTreeItemData back to the PyObject.
         PyObject* obj;
-        if (sipCpp == NULL) {
-            obj = Py_None;
-        } else {            
-            wxPyTreeItemData* data = static_cast<wxPyTreeItemData*>(sipCpp); 
-            obj = data->m_obj;
-        }
-        Py_INCREF(obj);
+        obj = wxPyTreeItemData::SafeGetData(static_cast<wxPyTreeItemData*>(sipCpp));
         return obj;
     %End
     
diff --git a/src/userdata.sip b/src/userdata.sip
index 7c95498b..918f9ce9 100644
--- a/src/userdata.sip
+++ b/src/userdata.sip
@@ -11,36 +11,15 @@
 
 
 %ModuleHeaderCode
-    // A wxPyUserData object that holds a reference to a Python object
-    class wxPyUserData : public wxObject 
-    {
-    public:
-        wxPyUserData() : wxObject()
-        {
-            m_obj = NULL;
-            m_incRef = false;
-        }
-        
-        wxPyUserData(PyObject* obj, bool incref=true) 
-        : wxObject()
-        {
-            m_obj = obj;
-            m_incRef = incref;
-            if (incref) {
-                wxPyBLOCK_THREADS( Py_INCREF(m_obj) );
-            }
-        }
-        virtual ~wxPyUserData() 
-        {
-            if (m_incRef) {
-                wxPyBLOCK_THREADS( Py_DECREF(m_obj) );
-            }
-            m_obj = NULL;
-        }
-        PyObject* m_obj;
-        bool      m_incRef;
-    };
- 
+// A wxObject object that holds a reference to a Python object
+class wxPyUserData : public wxPyUserDataHelper<wxObject>
+{
+public:
+    wxPyUserData(PyObject* obj = NULL)
+        : wxPyUserDataHelper<wxObject>(obj)
+    { }
+};
+
 %End
 
 
@@ -66,17 +45,8 @@
     %ConvertFromTypeCode
         // Code to convert a wxPyUserData back to the PyObject.
         PyObject* obj;
-        if (sipCpp == NULL) {
-            obj = Py_None;
-        } else {            
-            wxPyUserData* data = static_cast<wxPyUserData*>(sipCpp);  // TODO: verify pointer type?
-            obj = data->m_obj;
-        }
-        Py_INCREF(obj);
+        obj = wxPyUserData::SafeGetData(static_cast<wxPyUserData*>(sipCpp));
         return obj;
     %End
 };
 
-
-// NOTE TO SELF: It looks like the GIL is already held by the current thread
-// in ConvertToTypeCode and ConvertFromTypeCode code blocks...
diff --git a/src/wxpy_api.h b/src/wxpy_api.h
index 6744a30c..bb4844d2 100644
--- a/src/wxpy_api.h
+++ b/src/wxpy_api.h
@@ -213,5 +213,71 @@ private:
     wxPyBlock_t m_oldstate;
     bool        m_block;
 };
+  
+  
+//--------------------------------------------------------------------------
+// helper template to make common code for all of the various user data owners
+template<typename Base>
+class wxPyUserDataHelper : public Base {
+public:
+    explicit wxPyUserDataHelper(PyObject* obj = NULL) 
+        : m_obj(obj ? obj : Py_None) 
+    {
+        wxPyThreadBlocker blocker;
+        Py_INCREF(m_obj);   
+    }  
     
+    ~wxPyUserDataHelper()
+    {   // normally the derived class does the clean up, or deliberately leaks
+        // by setting m_obj to 0, but if not then do it here.
+        if (m_obj) {    
+            wxPyThreadBlocker blocker;
+            Py_DECREF(m_obj);
+            m_obj = 0;
+        }
+    }
+
+    // Return Value: New reference
+    PyObject* GetData() const {
+        wxPyThreadBlocker blocker;
+        Py_INCREF(m_obj);
+        return m_obj;
+    }
+    
+    // Return Value: Borrowed reference
+    PyObject* BorrowData() const {
+        return m_obj;
+    }
+
+    void SetData(PyObject* obj) {
+        if (obj != m_obj) {
+            wxPyThreadBlocker blocker;
+            Py_DECREF(m_obj);
+            m_obj = obj ? obj : Py_None;
+            Py_INCREF(m_obj);
+        }
+    }
+    
+    // Return the object in udata or None if udata is null
+    // Return Value: New reference
+    static PyObject* SafeGetData(wxPyUserDataHelper<Base>* udata) {
+        wxPyThreadBlocker blocker;
+        PyObject* obj = udata ? udata->BorrowData() : Py_None;
+        Py_INCREF(obj);
+        return obj;
+    }
+    
+    // Set the m_obj to null, this should only be used during clean up, when
+    // the object should be leaked.
+    // Calling any other methods on this object is then undefined behaviour
+    void ReleaseDataDuringCleanup()
+    {
+        m_obj = 0;        
+    }
+
+private:
+    PyObject* m_obj;
+};
+
+//--------------------------------------------------------------------------  
 #endif