--- a/mercurial/subrepo.py	Fri Apr 27 10:17:55 2012 +0200
+++ b/mercurial/subrepo.py	Fri Apr 27 11:02:16 2012 +0200
@@ -366,7 +366,7 @@
         pass
 
     def forget(self, ui, match, prefix):
-        return []
+        return ([], [])
 
     def revert(self, ui, substate, *pats, **opts):
         ui.warn('%s: reverting %s subrepos is unsupported\n' \