diff -r c547e1acc37c -r 361ab1e2086f mercurial/dirstate.py
--- a/mercurial/dirstate.py	Wed Oct 17 21:39:07 2012 -0500
+++ b/mercurial/dirstate.py	Wed Oct 17 21:42:06 2012 -0500
@@ -261,7 +261,7 @@
 
     def setbranch(self, branch):
         # no repo object here, just check for reserved names
-        scmutil.checknewlabel(None, branch)
+        scmutil.checknewlabel(None, branch, 'branch')
         self._branch = encoding.fromlocal(branch)
         f = self._opener('branch', 'w', atomictemp=True)
         try: