--- a/mercurial/commands.py	Thu May 23 17:53:19 2013 -0500
+++ b/mercurial/commands.py	Thu May 30 22:32:10 2013 +0100
@@ -1315,6 +1315,10 @@
         # 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

--- a/tests/test-graft.t	Thu May 23 17:53:19 2013 -0500
+++ b/tests/test-graft.t	Thu May 30 22:32:10 2013 +0100
@@ -174,6 +174,13 @@
   (use hg resolve and hg graft --continue)
   [255]
 
+Commit while interrupted should fail:
+
+  $ hg ci -m 'commit interrupted graft'
+  abort: cannot commit an interrupted graft operation
+  (use "hg graft -c" to continue graft)
+  [255]
+
 Continue without resolve should fail:
 
   $ hg graft -c