--- a/mercurial/worker.py	Sat Mar 10 15:50:09 2018 +0900
+++ b/mercurial/worker.py	Sat Mar 10 15:57:16 2018 +0900
@@ -176,7 +176,7 @@
                     os._exit(ret & 255)
         pids.add(pid)
     os.close(wfd)
-    fp = os.fdopen(rfd, pycompat.sysstr('rb'), 0)
+    fp = os.fdopen(rfd, r'rb', 0)
     def cleanup():
         signal.signal(signal.SIGINT, oldhandler)
         waitforworkers()