diff -r 1ef9b0b5efec -r 1447d3a9ff4a mercurial/commands.py
--- a/mercurial/commands.py	Wed Sep 08 13:48:25 2010 +0200
+++ b/mercurial/commands.py	Wed Sep 08 15:16:03 2010 +0200
@@ -338,7 +338,7 @@
             displayer.show(repo[nodes[0]])
             parents = repo[nodes[0]].parents()
             if len(parents) > 1:
-                side = state['bad'] if good else state['good']
+                side = good and state['bad'] or state['good']
                 num = len(set(i.node() for i in parents) & set(side))
                 if num == 1:
                     common = parents[0].ancestor(parents[1])