diff --git a/activesupport/lib/active_support/core_ext/class/attribute.rb b/activesupport/lib/active_support/core_ext/class/attribute.rb
index 83038f9da5..f2a221c396 100644
--- a/activesupport/lib/active_support/core_ext/class/attribute.rb
+++ b/activesupport/lib/active_support/core_ext/class/attribute.rb
@@ -118,7 +118,10 @@ class Class
   end
 
   private
-    def singleton_class?
-      ancestors.first != self
+
+    unless respond_to?(:singleton_class?)
+      def singleton_class?
+        ancestors.first != self
+      end
     end
 end