diff -r 78de43ab585f -r 48dea083f66d mercurial/worker.py
--- a/mercurial/worker.py	Thu Feb 09 15:20:41 2017 -0500
+++ b/mercurial/worker.py	Mon Feb 13 20:06:38 2017 +0530
@@ -157,7 +157,7 @@
                 os._exit(0)
         pids.add(pid)
     os.close(wfd)
-    fp = os.fdopen(rfd, 'rb', 0)
+    fp = os.fdopen(rfd, pycompat.sysstr('rb'), 0)
     def cleanup():
         signal.signal(signal.SIGINT, oldhandler)
         waitforworkers()