--- a/mercurial/subrepo.py	Wed Jan 14 20:29:47 2015 -0800
+++ b/mercurial/subrepo.py	Thu Jan 15 23:17:12 2015 +0100
@@ -614,7 +614,7 @@
             if defpath != defpushpath:
                 addpathconfig('default-push', defpushpath)
 
-            fp = self._repo.opener("hgrc", "w", text=True)
+            fp = self._repo.vfs("hgrc", "w", text=True)
             try:
                 fp.write(''.join(lines))
             finally: