Reverse post order on tag page.

Hey I know how to reverse the post order on categories.

<?php if (is_category(array(gigs))){
query_posts($query_string . "&order=ASC");} ?>

But now I want to reverse the post order of the posts that appear on a certain tag page.

For example this set of posts are reversed and im happy:
https://www.thewellleeds.com/category/gigs/

This set of posts are not reversed:
https://www.thewellleeds.com/tag/september/

Ive tried variations of the above code on archive.php but cant do it! HELP PLEASE ??