Keep non-members from posting comments with Paid Memberships Pro

my_pmpro_pre_comment_approved.php

//keep non-members from posting comments
function my_pmpro_pre_comment_approved($approved)
{
    if(function_exists('pmpro_hasMembershipLevel') && !pmpro_hasMembershipLevel())
        wp_die("Only members can post comments.");

    return $approved;
}
add_filter( 'pre_comment_approved', 'my_pmpro_pre_comment_approved' );