diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -2987,10 +2987,6 @@ class fullreposet(_spanset):
             # `other` was used with "&", let's assume this is a set like
             # object.
             other = baseset(other - self._hiddenrevs)
-        elif not util.safehasattr(other, 'isascending'):
-            # "other" is generatorset not a real smart set
-            # we fallback to the old way (sad kitten)
-            return super(fullreposet, self).__and__(other)
 
         if self.isascending():
             other.sort()