--- a/mercurial/subrepo.py	Wed May 08 14:11:01 2013 -0700
+++ b/mercurial/subrepo.py	Thu May 09 09:51:42 2013 -0400
@@ -31,7 +31,7 @@
 def _calcfilehash(filename):
     data = ''
     if os.path.exists(filename):
-        fd = open(filename)
+        fd = open(filename, 'rb')
         data = fd.read()
         fd.close()
     return util.sha1(data).hexdigest()