--- a/mercurial/discovery.py	Fri Jan 11 18:39:43 2013 +0100
+++ b/mercurial/discovery.py	Tue Jan 08 01:28:39 2013 +0100
@@ -196,7 +196,7 @@
     newmap = branchmap.branchcache((branch, heads[1])
                                  for branch, heads in headssum.iteritems()
                                  if heads[0] is not None)
-    newmap.update(repo, missingctx)
+    newmap.update(repo, (ctx.rev() for ctx in missingctx))
     for branch, newheads in newmap.iteritems():
         headssum[branch][1][:] = newheads
     return headssum