Query in category page doesn't work with tag

Here it’s what I have in category.php

<?php
if (have_posts()) : while (have_posts()) : the_post();
?>
CONTENT
<?php endwhile; endif; ?>

I want to show for each category only posts that have a specific tag=”big”

so I put right before CONTENT
<?php query_posts( 'tag=big' ); ?>

but suddenly it shows only the last recent post, which also doesn’t have the tag=big

What’s wrong?