diff -r a8d540d2628c -r 644a02f6b34f mercurial/pure/mpatch.py
--- a/mercurial/pure/mpatch.py	Wed Mar 14 14:05:45 2018 -0400
+++ b/mercurial/pure/mpatch.py	Wed Mar 14 11:52:35 2018 -0700
@@ -10,7 +10,7 @@
 import struct
 
 from .. import pycompat
-stringio = pycompat.stringio
+stringio = pycompat.bytesio
 
 class mpatchError(Exception):
     """error raised when a delta cannot be decoded