--- a/hgext/obsolete.py	Wed Jan 11 17:01:06 2012 +0100
+++ b/hgext/obsolete.py	Mon Jan 23 18:22:10 2012 +0100
@@ -302,6 +302,8 @@
                 sub = None
             if obj in self._obssubrels.get(sub, set()):
                 return 0
+            if sub == obj:
+                return 0
             self._obssubrels.setdefault(sub, set()).add(obj)
             self._obsobjrels.setdefault(obj, set()).add(sub)
             try: