--- a/mercurial/revset.py	Fri Sep 12 16:21:13 2014 -0700
+++ b/mercurial/revset.py	Fri Sep 12 15:00:51 2014 -0700
@@ -1236,7 +1236,7 @@
     cl = repo.changelog
     for r in getset(repo, spanset(repo), x):
         ps.update(cl.parentrevs(r))
-    return subset & ps
+    return baseset(ps) & subset
 
 def parentspec(repo, subset, x, n):
     """``set^0``