--- a/mercurial/mdiff.py	Thu Dec 15 14:59:22 2011 -0600
+++ b/mercurial/mdiff.py	Thu Dec 15 15:27:11 2011 -0600
@@ -318,7 +318,7 @@
 def patch(a, bin):
     if len(a) == 0:
         # skip over trivial delta header
-        return buffer(bin, 12)
+        return util.buffer(bin, 12)
     return mpatch.patches(a, [bin])
 
 # similar to difflib.SequenceMatcher.get_matching_blocks