Loop in sidebar show all post instead of the last 10 when viewing singel post

Ok, so, I’m running this loop to get the latest posts in my sidebar…

<?php $archive_query = new WP_Query('showposts=10'); while ($archive_query->have_posts()) : $archive_query->the_post(); ?>
    <li><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a><br /><span>Postat <?php the_time('l j F, Y'); ?></span></li>
<?php endwhile; ?>

…and it works fine when I’am on index but as soon as I go to a singel post view it doesn’t work, it print’s out ALL the post, not just the last 10!

Anyone know what the problem might be?