--- a/mercurial/revset.py	Wed Oct 08 02:48:24 2014 -0700
+++ b/mercurial/revset.py	Wed Oct 08 02:48:56 2014 -0700
@@ -1042,7 +1042,7 @@
     except (TypeError, ValueError):
         # i18n: "last" is a keyword
         raise error.ParseError(_("last expects a number"))
-    ss = subset.set()
+    ss = subset
     os = getset(repo, spanset(repo), l[0])
     os.reverse()
     result = []