diff -r ae92c3eee88e -r 0d83ad967bf8 mercurial/exchange.py
--- a/mercurial/exchange.py	Fri Jun 10 00:25:07 2016 -0400
+++ b/mercurial/exchange.py	Fri Jun 10 00:12:33 2016 -0400
@@ -8,6 +8,7 @@
 from __future__ import absolute_import
 
 import errno
+import hashlib
 
 from .i18n import _
 from .node import (
@@ -1646,7 +1647,7 @@
     Used by peer for unbundling.
     """
     heads = repo.heads()
-    heads_hash = util.sha1(''.join(sorted(heads))).digest()
+    heads_hash = hashlib.sha1(''.join(sorted(heads))).digest()
     if not (their_heads == ['force'] or their_heads == heads or
             their_heads == ['hashed', heads_hash]):
         # someone else committed/pushed/unbundled while we