mercurial/revset.py

--- a/mercurial/revset.py	Wed Sep 17 10:58:50 2014 -0700
+++ b/mercurial/revset.py	Wed Sep 17 10:59:16 2014 -0700
@@ -834,7 +834,7 @@
     else:
         s = _revancestors(repo, baseset([c.rev()]), followfirst)
 
-    return subset.filter(s.__contains__)
+    return subset & s
 
 def follow(repo, subset, x):
     """``follow([file])``