diff -r e6d3d39cc1c7 -r d3e761f9ac0a mercurial/localrepo.py
--- a/mercurial/localrepo.py	Wed Sep 19 11:38:05 2018 -0700
+++ b/mercurial/localrepo.py	Wed Sep 19 16:15:22 2018 -0700
@@ -2792,7 +2792,7 @@
     if unknownopts:
         raise error.Abort(_('unable to create repository because of unknown '
                             'creation option: %s') %
-                          ', '.sorted(unknownopts),
+                          ', '.join(sorted(unknownopts)),
                           hint=_('is a required extension not loaded?'))
 
     requirements = newreporequirements(ui, createopts=createopts)