diff -r 4015dfc899bb -r 73b3bee8febe mercurial/pycompat.py
--- a/mercurial/pycompat.py	Sun Mar 12 00:48:06 2017 -0500
+++ b/mercurial/pycompat.py	Mon Mar 13 00:55:14 2017 +0530
@@ -55,6 +55,7 @@
     sysexecutable = sys.executable
     if sysexecutable:
         sysexecutable = os.fsencode(sysexecutable)
+    stringio = io.BytesIO
 
     # TODO: .buffer might not exist if std streams were replaced; we'll need
     # a silly wrapper to make a bytes stream backed by a unicode one.
@@ -180,8 +181,8 @@
     getcwd = os.getcwd
     sysexecutable = sys.executable
     shlexsplit = shlex.split
+    stringio = io.StringIO
 
-stringio = io.StringIO
 empty = _queue.Empty
 queue = _queue.Queue