--- a/vregistry.py	Tue Jun 09 18:30:42 2009 +0200
+++ b/vregistry.py	Tue Jun 09 18:46:20 2009 +0200
@@ -216,7 +216,8 @@
         # registered() is technically a classmethod but is not declared
         # as such because we need to compose registered in some cases
         vobject = obj.registered.im_func(obj, self)
-        assert not vobject in vobjects, vobject
+        assert not vobject in vobjects, vobject, \
+               'object %s is already registered' % vobject
         assert callable(vobject.__select__), vobject
         vobjects.append(vobject)
         try: