diff -r c6666395fdd2 -r de32e9881698 mercurial/bundle2.py
--- a/mercurial/bundle2.py	Fri Feb 06 23:40:46 2015 +0100
+++ b/mercurial/bundle2.py	Thu Feb 05 15:52:57 2015 -0800
@@ -497,7 +497,7 @@
         """read exactly <size> bytes from the stream"""
         return changegroup.readexactly(self._fp, size)
 
-    def seek(self, offset, whence):
+    def seek(self, offset, whence=0):
         """move the underlying file pointer"""
         if self._seekable:
             return self._fp.seek(offset, whence)