diff -r 43d55088415a -r 67964cda8701 mercurial/revlog.py
--- a/mercurial/revlog.py	Sat May 12 16:00:53 2012 +0200
+++ b/mercurial/revlog.py	Sat May 12 16:00:57 2012 +0200
@@ -1208,7 +1208,7 @@
                     continue
 
                 for p in (p1, p2):
-                    if not p in self.nodemap:
+                    if p not in self.nodemap:
                         raise LookupError(p, self.indexfile,
                                           _('unknown parent'))