Sorting custom admin column by value

Ah, the remedy was a simple one:

function issue_column_orderby( $vars ) {
    if ( isset( $vars['orderby'] ) && 'linked_issue_post' == $vars['orderby'] ) {       
        $vars = array_merge( $vars, array(
            'meta_key' => 'article_issue_n',
            'orderby' => 'meta_value'
        ) );
    }

    return $vars;
}
add_filter( 'request', 'issue_column_orderby' );

I probably omitted something before…