diff -r d036ea711140 -r 7e4f66fe964b mercurial/merge.py
--- a/mercurial/merge.py	Sun Mar 02 08:51:02 2008 -0800
+++ b/mercurial/merge.py	Fri Mar 14 11:01:31 2008 -0500
@@ -106,7 +106,7 @@
             seen[s] = 1
             if fc.path() != orig and fc.path() not in old:
                 old[fc.path()] = 1
-            if fc.rev() < limit:
+            if fc.rev() < limit and fc.rev() is not None:
                 continue
             visit += fc.parents()