diff -r 372f507f6676 -r d7ab5684711f mercurial/revset.py
--- a/mercurial/revset.py	Wed Oct 01 15:50:40 2014 -0500
+++ b/mercurial/revset.py	Wed Oct 01 15:50:54 2014 -0500
@@ -2817,8 +2817,6 @@
                               ascending=self.isascending())
 
     def __sub__(self, x):
-        if isinstance(x, baseset):
-            x = x.set()
         filterfunc = x.__contains__
         return orderedlazyset(self, lambda r: not filterfunc(r),
                               ascending=self.isascending())