--- a/mercurial/bundle2.py	Mon Apr 21 18:59:09 2014 -0700
+++ b/mercurial/bundle2.py	Mon Apr 21 20:04:54 2014 -0700
@@ -730,7 +730,8 @@
         h = inpart.read(20)
     assert not h
     if heads != op.repo.heads():
-        raise error.PushRaced()
+        raise error.PushRaced('repository changed while pushing - '
+                              'please try again')
 
 @parthandler('b2x:output')
 def handleoutput(op, inpart):