function wpse32738_get_editable_roles( $editable_roles )
	{
		global $wp_roles;
	    if ( current_user_can( 'manage_options' ) ) {
	    	unset($role_names['administrator']);
	    }

	    return $editable_roles;
	}
	add_filter( 'editable_roles', 'wpse32738_get_editable_roles' );