Laravel 4 - Artisan error SQLSTATE[42000]

I am trying to create a new migration for my users table, I have the following schema: ``` Schema::create('users', function($t) { $t->increments('id'); $t->string('username', 16); $t->string('password', 64); $t->integer('role', 64); $t->timestamps(); }); ``` When I try to run php artisan migrate from the terminal, I get the following error: [Exception] SQLSTATE[42000]: Syntax error or access violation: 1075 Incorrect table definition; there can be only one auto column and it must be defined as a key (SQL: create table `users` (`id` int unsigne d not null auto_increment primary key, `username` varchar(16) not null, `password` varchar(64) no t null, `role` int not null auto_increment primary key, `created_at` timestamp default 0 not null , `updated_at` timestamp default 0 not null)) (Bindings: array ( )) The error has something to do with the 'role' field, as when this is removed it seems to run fine. Thanks in advance for any help or insight.