How to display firstname in showlistings.tpl

Hi!

I am trying to display the full name of the owners of the listings on the category.php page, so I added the following line to the showlistings.tpl page:

<td{if $entry.class<>""} class="{$entry.class}"{/if}>{$entry.lastname} {$entry.firstname}</td>

However, for some reason, the above solution does not work. If I replace the above with the following lines instead:

<td{if $entry.class<>""} class="{$entry.class}"{/if}>{$entry.username}</td>

then it displays the username perfectly.

Any idea, why the full name does not work correctly?

Thank you!
Vert