--- a/mercurial/statichttprepo.py	Thu Jun 02 00:33:33 2011 +0200
+++ b/mercurial/statichttprepo.py	Fri Jun 03 20:08:26 2011 +0200
@@ -124,7 +124,7 @@
         self._branchcachetip = None
         self.encodepats = None
         self.decodepats = None
-        self.capabilities = self.capabilities.difference(["pushkey"])
+        self.capabilities.difference_update(["pushkey"])
 
     def url(self):
         return self._url