diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2183,8 +2183,13 @@
         # read in unfinished revisions
         if cmdstate:
             cmdstate.load()
-            nodes = cmdstate['nodes']
-            revs = [repo[node].rev() for node in nodes]
+            if cmdstate['version'] < 2:
+                nodes = cmdstate['nodes']
+                revs = [repo[node].rev() for node in nodes]
+            else:
+                # state-file is written by a newer mercurial than what we are
+                # using
+                raise error.Abort(_("unable to read to read the state file"))
         else:
             cmdutil.wrongtooltocontinue(repo, _('graft'))
     else:
@@ -2311,7 +2316,7 @@
             if stats[3] > 0:
                 # write out state for --continue
                 nodelines = [repo[rev].hex() for rev in revs[pos:]]
-                cmdstate.addopts({'nodes': nodelines})
+                cmdstate.addopts({'version': 1, 'nodes': nodelines})
                 cmdstate.save()
                 extra = ''
                 if opts.get('user'):
diff --git a/mercurial/state.py b/mercurial/state.py
--- a/mercurial/state.py
+++ b/mercurial/state.py
@@ -117,4 +117,4 @@
 @readoldstatefile('graftstate')
 def oldgraftstate(fp):
     nodes = fp.read().splitlines()
-    return {'nodes': nodes}
+    return {'version': 0, 'nodes': nodes}