diff --git a/lib/sorted_set.rb b/lib/sorted_set.rb
index 305f60b..7ca5fa7 100644
--- a/lib/sorted_set.rb
+++ b/lib/sorted_set.rb
@@ -51,7 +51,7 @@
 class SortedSet < Set
   # Creates a SortedSet.  See Set.new for details.
   def initialize(*args)
-    @hash = RBTree.new
+    @hash = RBTree.new(false)
     super
   end
 end
diff --git a/test/test_sorted_set.rb b/test/test_sorted_set.rb
index 3b7622a..6b091e2 100644
--- a/test/test_sorted_set.rb
+++ b/test/test_sorted_set.rb
@@ -46,6 +46,10 @@ def test_sortedset
     assert_same(nil, ret)
     assert_equal(['four', 'one', 'three', 'two'], s.to_a)
     assert_equal(['four', 'one', 'three', 'two'], a)
+
+    s = SortedSet.new([1,2,3])
+    assert_equal(true, s.include?(1))
+    assert_equal(false, s.include?(5))
   end
 
   def test_each