diff -r 9e9c407e0d1f -r 043abd6a91d1 mercurial/commands.py
--- a/mercurial/commands.py	Mon May 27 15:24:19 2013 -0500
+++ b/mercurial/commands.py	Sat Jun 01 17:19:00 2013 -0500
@@ -1330,6 +1330,10 @@
         # Let --subrepos on the command line override config setting.
         ui.setconfig('ui', 'commitsubrepos', True)
 
+    if repo.vfs.exists('graftstate'):
+        raise util.Abort(_('cannot commit an interrupted graft operation'),
+                         hint=_('use "hg graft -c" to continue graft'))
+
     extra = {}
     if opts.get('close_branch'):
         extra['close'] = 1