diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index 6c2403d87e..b9141b9b33 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -66,6 +66,7 @@ module ActiveRecord
       # Generates all the attribute related methods for columns in the database
       # accessors, mutators and query methods.
       def define_attribute_methods # :nodoc:
+        return false if @attribute_methods_generated
         # Use a mutex; we don't want two thread simultaneously trying to define
         # attribute methods.
         generated_attribute_methods.synchronize do