diff -r 9fe8e1e80841 -r e15027cc4cd8 mercurial/revset.py
--- a/mercurial/revset.py	Fri Oct 10 13:31:00 2014 -0700
+++ b/mercurial/revset.py	Wed Oct 08 02:50:20 2014 -0700
@@ -1478,8 +1478,8 @@
     """``roots(set)``
     Changesets in set with no parent changeset in set.
     """
-    s = getset(repo, spanset(repo), x).set()
-    subset = baseset([r for r in s if r in subset.set()])
+    s = getset(repo, spanset(repo), x)
+    subset = baseset([r for r in s if r in subset])
     cs = _children(repo, subset, s)
     return subset - cs