I am trying to add a unique index that gets created from the foreign keys of four associated tables: add_index :studies, ["user_id", "university_id", "subject_name_id", "subject_type_id"], :unique => true The database’s limitation for the index name causes the migration to fail. Here’s the error message: Index name 'index_studies_on_user_id_and_university_id_and_subject_name_id_and_subject_type_id