diff -r 874712506b07 -r c31ce080eb75 mercurial/debugcommands.py
--- a/mercurial/debugcommands.py	Fri Sep 21 21:14:27 2018 -0400
+++ b/mercurial/debugcommands.py	Sun Sep 23 00:47:04 2018 -0400
@@ -3074,7 +3074,8 @@
             '-R', repo.root,
             'debugserve', '--sshstdio',
         ]
-        proc = subprocess.Popen(args, stdin=subprocess.PIPE,
+        proc = subprocess.Popen(pycompat.rapply(procutil.tonativestr, args),
+                                stdin=subprocess.PIPE,
                                 stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                                 bufsize=0)