diff --git a/mercurial/branchmap.py b/mercurial/branchmap.py
--- a/mercurial/branchmap.py
+++ b/mercurial/branchmap.py
@@ -211,7 +211,7 @@
 
     def __init__(self, entries=(), tipnode=nullid, tiprev=nullrev,
                  filteredhash=None, closednodes=None):
-        super(branchcache, self).__init__(entries)
+        super(_branchcache, self).__init__(entries)
         self.tipnode = tipnode
         self.tiprev = tiprev
         self.filteredhash = filteredhash
@@ -369,6 +369,11 @@
         self.write(repo)
 
 
+# keep a private reference to the class object so that subclasses that
+# replace the branchcache class do not break super()
+_branchcache = branchcache
+
+
 class remotebranchcache(branchcache):
     """Branchmap info for a remote connection, should not write locally"""
     def write(self, repo):