diff -r 1527f40de3b3 -r 5bc7ff103081 mercurial/wireproto.py
--- a/mercurial/wireproto.py	Sat Mar 10 15:50:09 2018 +0900
+++ b/mercurial/wireproto.py	Sat Mar 10 15:57:16 2018 +0900
@@ -1027,7 +1027,7 @@
 
             # write bundle data to temporary file because it can be big
             fd, tempname = tempfile.mkstemp(prefix='hg-unbundle-')
-            fp = os.fdopen(fd, pycompat.sysstr('wb+'))
+            fp = os.fdopen(fd, r'wb+')
             r = 0
             try:
                 proto.forwardpayload(fp)