"instance_methods" includes public and protected

activerecord/lib/active_record/attribute_methods.rb

@@ -18,7 +18,7 @@ def define_attribute_methods
       # method is defined by Active Record though.
       def instance_method_already_implemented?(method_name)
         method_name = method_name.to_s
-        @_defined_class_methods         ||= ancestors.first(ancestors.index(ActiveRecord::Base)).sum([]) { |m| m.public_instance_methods(false) | m.private_instance_methods(false) | m.protected_instance_methods(false) }.map {|m| m.to_s }.to_set
+        @_defined_class_methods         ||= ancestors.first(ancestors.index(ActiveRecord::Base)).sum([]) { |m| m.instance_methods(false) | m.private_instance_methods(false) }.map {|m| m.to_s }.to_set
         @@_defined_activerecord_methods ||= defined_activerecord_methods
         raise DangerousAttributeError, "#{method_name} is defined by ActiveRecord" if @@_defined_activerecord_methods.include?(method_name)
         @_defined_class_methods.include?(method_name)