--- a/mercurial/revset.py	Fri Jan 31 01:12:35 2014 -0800
+++ b/mercurial/revset.py	Thu Feb 06 08:31:55 2014 -0800
@@ -522,7 +522,7 @@
     """
     # i18n: "closed" is a keyword
     getargs(x, 0, 0, _("closed takes no arguments"))
-    return baseset([r for r in subset if repo[r].closesbranch()])
+    return lazyset(subset, lambda r: repo[r].closesbranch())
 
 def contains(repo, subset, x):
     """``contains(pattern)``