Wrong archive link when using the_terms

I want to display a custom taxonomy on single posts, with a link to the archive page for that term. I use this code:

<?php the_terms( $post->ID, 'taxonomyname' ); ?>

It displays correctly the terms associated to that post. The link I get is: wordpress/?taxonomy=taxonomyname&term=taxonomyterm

That link doesn’t work. I have pretty permalinks, multisite, and the correct link for that archive is: wordpress/blog/taxonomyname/taxonomyterm/.

I’m using a custom child theme of Twenty eleven.

What could I do? Thanks.