diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -747,6 +747,8 @@ def _dispatch(req):
         if options['verbose'] or options['debug'] or options['quiet']:
             for opt in ('verbose', 'debug', 'quiet'):
                 val = str(bool(options[opt]))
+                if pycompat.ispy3:
+                    val = val.encode('ascii')
                 for ui_ in uis:
                     ui_.setconfig('ui', opt, val, '--' + opt)