Index: gtk/pygtkcellrenderer.c
===================================================================
--- gtk/pygtkcellrenderer.c	(revision 2964)
+++ gtk/pygtkcellrenderer.c	(working copy)
@@ -250,7 +250,8 @@ pygtk_generic_cell_renderer_activate (Gt
     Py_DECREF(py_ret);
 
 out:
-    pygtk_boxed_unref_shared(py_event);
+    if (py_event != Py_None)
+        pygtk_boxed_unref_shared(py_event);
     Py_DECREF(py_widget);
     Py_DECREF(py_background_area);
     Py_DECREF(py_cell_area);
