function bbp_user_add_role_on_register( $user_id = '' ) {

	// Posted role
	$forum_role = isset( $_POST['bbp-forums-role'] )
		? sanitize_key( $_POST['bbp-forums-role'] )
		: bbp_get_default_role();

	// Role keys
	$roles = array_keys( bbp_get_dynamic_roles() );

	// Bail if posted role is not in dynamic roles
	if ( empty( $forum_role ) || ! in_array( $forum_role, $roles, true ) ) {
		return;
	}

	// Set the user role
	bbp_set_user_role( $user_id, $forum_role );
}