diff -r 1fce478552b8 -r 54feb8d3bab7 mercurial/commands.py
--- a/mercurial/commands.py	Fri Aug 24 14:52:45 2012 -0500
+++ b/mercurial/commands.py	Fri Aug 24 14:53:07 2012 -0500
@@ -4269,7 +4269,7 @@
                              hint=_("run 'hg heads .' to see heads"))
 
         parent = repo.dirstate.p1()
-        if len(nbhs) == 1:
+        if len(nbhs) <= 1:
             if len(bheads) > 1:
                 raise util.Abort(_("heads are bookmarked - "
                                    "please merge with an explicit rev"),