dbDelta: Issues with upgrading tables with composite primary key

I typically don’t have any issues with dbDelta. However, I came across a problem during upgrade that has to do with using a composite primary key. The first time the below code is run, the table is deployed with no errors. However, the moment I run deployment again with dbDelta, it bombs out. I’m currently on 3.3.1.

Code:
require_once(ABSPATH . ‘wp-admin/includes/upgrade.php’);

function yobik_whatupwiththis () {
	global $wpdb;

	$sql[] = "CREATE TABLE my_table (
		yo_id int(11) NOT NULL default 0,
		bik_id smallint(6) NOT NULL default 0,
		wha_id smallint(6) NOT NULL default 0,
		tus_id smallint(6) NOT NULL default 0,
		PRIMARY KEY (yo_id, bik_id))";

	dbDelta($sql);
}

Resulting Error:
WordPress database error: [Multiple primary key defined]
ALTER TABLE my_table ADD PRIMARY KEY (yo_id, bik_id)

Wondering if somebody has come across this issue.

Thanks in advance.