--- a/mercurial/revset.py	Fri Oct 10 11:27:04 2014 -0700
+++ b/mercurial/revset.py	Fri Oct 10 12:30:56 2014 -0700
@@ -2313,10 +2313,13 @@
         if not isinstance(data, list):
             data = list(data)
         self._list = data
-        self._set = None
         self._ascending = None
 
     @util.propertycache
+    def _set(self):
+        return set(self._list)
+
+    @util.propertycache
     def _asclist(self):
         asclist = self._list[:]
         asclist.sort()