diff --git a/contrib/revsetbenchmarks.txt b/contrib/revsetbenchmarks.txt
--- a/contrib/revsetbenchmarks.txt
+++ b/contrib/revsetbenchmarks.txt
@@ -23,4 +23,5 @@ draft()
 max(::(tip~20) - obsolete())
 roots((0:tip)::)
 (not public() - obsolete())
+parents(20000)
 (20000::) - (20000)
diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -1236,7 +1236,7 @@ def parents(repo, subset, x):
     cl = repo.changelog
     for r in getset(repo, spanset(repo), x):
         ps.update(cl.parentrevs(r))
-    return subset & ps
+    return baseset(ps) & subset
 
 def parentspec(repo, subset, x, n):
     """``set^0``
diff --git a/tests/test-revset.t b/tests/test-revset.t
--- a/tests/test-revset.t
+++ b/tests/test-revset.t
@@ -567,10 +567,10 @@ test subtracting something from an addse
 test intersecting something with an addset
 
   $ log 'parents(outgoing() or removes(a))'
+  8
   1
   4
   5
-  8
 
 check that conversion to only works
   $ try --optimize '::3 - ::1'