--- a/mercurial/cmdutil.py	Thu Dec 27 23:55:39 2007 -0600
+++ b/mercurial/cmdutil.py	Thu Dec 27 23:55:39 2007 -0600
@@ -64,6 +64,8 @@
     raise UnknownCommand(cmd)
 
 def bail_if_changed(repo):
+    if repo.dirstate.parents()[1] != nullid:
+        raise util.Abort(_('outstanding uncommitted merge'))
     modified, added, removed, deleted = repo.status()[:4]
     if modified or added or removed or deleted:
         raise util.Abort(_("outstanding uncommitted changes"))