Почему не устанавливается внешний ключ?

Table: role
Columns:
id_role int(11) AI PK 
role varchar(45)

Table: users
Columns:
id_user int(11) AI PK 
username varchar(45) 
password varchar(45) 
role int(11) PK 
department int(11) PK

Executing:
ALTER TABLE `moysclad`.`role` 
ADD CONSTRAINT `id`
  FOREIGN KEY (`id_role`)
  REFERENCES `moysclad`.`users` (`role`)
  ON DELETE NO ACTION
  ON UPDATE NO ACTION;

Operation failed: There was an error while applying the SQL script to the database.
ERROR 1215: Cannot add foreign key constraint
SQL Statement:
ALTER TABLE `moysclad`.`role` 
ADD CONSTRAINT `id`
  FOREIGN KEY (`id_role`)
  REFERENCES `moysclad`.`users` (`role`)
  ON DELETE NO ACTION
  ON UPDATE NO ACTION