What is wrong with my SQL here 1089 - Incorrect prefix key

Question

CREATE TABLE `table`.`users` (
    `id` INT(11) NOT NULL AUTO_INCREMENT,
    `username` VARCHAR(50) NOT NULL,
    `password` VARCHAR(50) NOT NULL,
    `dir` VARCHAR(100) NOT NULL,
    PRIMARY KEY (`id`(11))
) ENGINE = MyISAM;

I'm getting the #1089 - Incorrect prefix key error and can't figure out what I'm doing wrong.