diff -r 40852b4b910c -r 4cdaf1adafc8 mercurial/ancestor.py
--- a/mercurial/ancestor.py	Fri Sep 24 12:00:55 2010 +0200
+++ b/mercurial/ancestor.py	Fri Sep 24 12:46:54 2010 -0500
@@ -34,7 +34,7 @@
             visit.pop()
         else:
             for p in pl:
-                if p in (a, b): # did we find a or b as a parent?
+                if p == a or p == b: # did we find a or b as a parent?
                     return p # we're done
                 if p not in depth:
                     visit.append(p)