diff -r eca468b8fae4 -r a91d7dfd1952 mercurial/changegroup.py
--- a/mercurial/changegroup.py	Tue Sep 15 17:53:28 2015 -0700
+++ b/mercurial/changegroup.py	Tue Sep 15 17:43:54 2015 -0700
@@ -119,7 +119,7 @@
             bundle = bundle2.bundle20(ui)
             part = bundle.newpart('changegroup', data=cg.getchunks())
             part.addparam('version', cg.version)
-            z = util.compressors['UN']()
+            z = util.compressors[None]()
             chunkiter = bundle.getchunks()
         else:
             if cg.version != '01':