diff --git a/mercurial/sshpeer.py b/mercurial/sshpeer.py
--- a/mercurial/sshpeer.py
+++ b/mercurial/sshpeer.py
@@ -220,7 +220,7 @@
 
     # Generate a random token to help identify responses to version 2
     # upgrade request.
-    token = bytes(uuid.uuid4())
+    token = pycompat.sysbytes(str(uuid.uuid4()))
     upgradecaps = [
         ('proto', wireprotoserver.SSHV2),
     ]