mercurial/revset.py

--- a/mercurial/revset.py	Thu Oct 16 14:46:37 2014 -0700
+++ b/mercurial/revset.py	Tue Sep 30 15:03:54 2014 -0500
@@ -347,7 +347,7 @@
     if not heads:
         return baseset()
     s = _revancestors(repo, heads, followfirst)
-    return subset.filter(s.__contains__)
+    return subset & s
 
 def ancestors(repo, subset, x):
     """``ancestors(set)``