--- a/mercurial/branchmap.py	Sun Mar 12 03:32:21 2017 -0400
+++ b/mercurial/branchmap.py	Sun Mar 12 00:49:19 2017 -0500
@@ -409,7 +409,7 @@
         # fast path: extract data from cache, use it if node is matching
         reponode = changelog.node(rev)[:_rbcnodelen]
         cachenode, branchidx = unpack(
-            _rbcrecfmt, buffer(self._rbcrevs, rbcrevidx, _rbcrecsize))
+            _rbcrecfmt, util.buffer(self._rbcrevs, rbcrevidx, _rbcrecsize))
         close = bool(branchidx & _rbccloseflag)
         if close:
             branchidx &= _rbcbranchidxmask