diff --git a/src/about_objects.rb b/src/about_objects.rb
index 0d752583..4d9b15d9 100644
--- a/src/about_objects.rb
+++ b/src/about_objects.rb
@@ -21,7 +21,7 @@ def test_objects_can_be_inspected
 
   def test_every_object_has_an_id
     obj = Object.new
-    assert_equal __(Fixnum), obj.object_id.class
+    assert obj.object_id.is_a?(__(Integer))
   end
 
   def test_every_object_has_different_id