diff --git a/mercurial/subrepo.py b/mercurial/subrepo.py
index b37d5ecc22276cb17faac0e9a6a2d1c344a8fb01_bWVyY3VyaWFsL3N1YnJlcG8ucHk=..e7d45e41338c234785e38c02e2ee47432376a352_bWVyY3VyaWFsL3N1YnJlcG8ucHk= 100644
--- a/mercurial/subrepo.py
+++ b/mercurial/subrepo.py
@@ -220,7 +220,7 @@
         """
         raise NotImplementedError
 
-    def checknested(path):
+    def checknested(self, path):
         """check if path is a subrepository within this repository"""
         return False