query_posts tags and categories

I intend to list posts from a specific category for a specific tag.

The following outputs nothing (before loop):

<?php query_posts("cat=1&tag=tagtest"); ?>

.. so I do the filtering inside the loop:

<?php query_posts("tag=tagtest"); ?>
loop starts here
<?php if (in_category(1)){ ?>
the output <?php } ?>
loop ends here

Is there a more elegant way for this?
Why does query_posts("cat=1&tag=tagtest"); not work?