--- a/mercurial/revset.py	Thu Oct 09 20:15:41 2014 -0700
+++ b/mercurial/revset.py	Thu Oct 09 09:12:54 2014 -0700
@@ -664,10 +664,15 @@
 
     # Both sets need to be ascending in order to lazily return the union
     # in the correct order.
-    args.sort()
-    result = (filteredset(s, subset.__contains__, ascending=True) +
-              filteredset(args, subset.__contains__, ascending=True))
-
+    base = subset & args
+    desc = subset & s
+    result = base + desc
+    if subset.isascending():
+        result.sort()
+    elif subset.isdescending():
+        result.sort(reverse=True)
+    else:
+        result = subset & result
     return result
 
 def descendants(repo, subset, x):