bug.diff

diff --git a/activerecord/lib/active_record/attribute_methods/write.rb b/activerecord/lib/active_record/attribute_methods/write.rb
index 6a593a7..832f2ed 100644
--- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -10,7 +10,9 @@ module ActiveRecord
       module ClassMethods
         protected
           def define_method_attribute=(attr_name)
-            generated_attribute_methods.module_eval("def #{attr_name}=(new_value); write_attribute('#{attr_name}', new_value); end", __FILE__, __LINE__)
+            generated_attribute_methods.send(:define_method, "#{attr_name}=") do |new_value|
+              write_attribute(attr_name, new_value)
+            end
           end
       end