diff -r 1527f40de3b3 -r 5bc7ff103081 mercurial/httppeer.py
--- a/mercurial/httppeer.py	Sat Mar 10 15:50:09 2018 +0900
+++ b/mercurial/httppeer.py	Sat Mar 10 15:57:16 2018 +0900
@@ -459,7 +459,7 @@
         try:
             # dump bundle to disk
             fd, filename = tempfile.mkstemp(prefix="hg-bundle-", suffix=".hg")
-            fh = os.fdopen(fd, pycompat.sysstr("wb"))
+            fh = os.fdopen(fd, r"wb")
             d = fp.read(4096)
             while d:
                 fh.write(d)