--- a/appobject.py	Fri Feb 26 09:54:32 2010 +0100
+++ b/appobject.py	Fri Feb 26 13:09:12 2010 +0100
@@ -268,7 +268,7 @@
             pdef['default'] = getattr(cls, propid, pdef['default'])
             pdef['sitewide'] = getattr(cls, 'site_wide', pdef.get('sitewide'))
             registry.vreg.register_property(cls._cwpropkey(propid), **pdef)
-        assert callable(cls.__select__), obj
+        assert callable(cls.__select__), cls
         return cls
 
     def __init__(self, req, **extra):