diff --git a/mercurial/hgweb/server.py b/mercurial/hgweb/server.py
--- a/mercurial/hgweb/server.py
+++ b/mercurial/hgweb/server.py
@@ -275,7 +275,7 @@ def create_server(ui, repo):
 
         def __init__(self, *args, **kwargs):
             if self.address_family is None:
-                raise RepoError(_('IPv6 not available on this system'))
+                raise error.RepoError(_('IPv6 not available on this system'))
             super(IPv6HTTPServer, self).__init__(*args, **kwargs)
 
     if ssl_cert: