diff --git a/contrib/all-revsets.txt b/contrib/all-revsets.txt
--- a/contrib/all-revsets.txt
+++ b/contrib/all-revsets.txt
@@ -23,8 +23,6 @@ parents(20000)
 # Used in revision 911f5a6579d1
 p1(20000)
 p2(10000)
-# Used in revision f140d6207cca
-roots(0:tip)
 # Used in revision b6dc3b79bb25
 0::
 # Used in revision faf4f63533ff
@@ -101,15 +99,12 @@ draft()
 ::tip
 draft() and ::tip
 ::tip and draft()
-roots(0::tip)
 author(lmoscovicz)
 author(mpm)
-42:68 and roots(42:tip)
 ::p1(p1(tip))::
 public()
 :10000 and public()
 :10000 and draft()
-roots((0:tip)::)
 (not public() - obsolete())
 
 # The one below is used by rebase
@@ -119,6 +114,18 @@ roots((0:tip)::)
 roots((tip~100::) - (tip~100::tip))
 roots((0::) - (0::tip))
 
+# more roots testing
+roots(tip~100:)
+roots(:42)
+roots(not public())
+roots((0:tip)::)
+roots(0::tip)
+42:68 and roots(42:tip)
+# Used in revision f140d6207cca
+roots(0:tip)
+# test disjoint set with multiple roots
+roots((:42) + (tip~42:))
+
 # Testing the behavior of "head()" in various situations
 head()
 head() - public()
diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -1755,9 +1755,13 @@ def roots(repo, subset, x):
     Changesets in set with no parent changeset in set.
     """
     s = getset(repo, fullreposet(repo), x)
-    subset = subset & s# baseset([r for r in s if r in subset])
-    cs = _children(repo, subset, s)
-    return subset - cs
+    parents = repo.changelog.parentrevs
+    def filter(r):
+        for p in parents(r):
+            if 0 <= p and p in s:
+                return False
+        return True
+    return subset & s.filter(filter)
 
 def sort(repo, subset, x):
     """``sort(set[, [-]key...])``