diff -r 464539c305aa -r 3db545fccac1 mercurial/extensions.py
--- a/mercurial/extensions.py	Fri Nov 27 19:35:37 2020 -0500
+++ b/mercurial/extensions.py	Fri Nov 27 14:54:37 2020 -0500
@@ -936,6 +936,10 @@
         version = b''
     if isinstance(version, (list, tuple)):
         version = b'.'.join(pycompat.bytestr(o) for o in version)
+    else:
+        # version data should be bytes, but not all extensions are ported
+        # to py3.
+        version = stringutil.forcebytestr(version)
     return version