diff --git a/viewtopic.php b/viewtopic.php
index 5583791ec..fc3d22f1e 100644
--- a/viewtopic.php
+++ b/viewtopic.php
@@ -594,7 +594,7 @@ $this_date = bb_date(TIMENOW, 'md', false);
 for ($i = 0; $i < $total_posts; $i++) {
     $poster_id = $postrow[$i]['user_id'];
     $poster = ($poster_id == GUEST_UID) ? $lang['GUEST'] : $postrow[$i]['username'];
-    $poster_birthday = ($poster_id != GUEST_UID) ? date('md', strtotime($postrow[$i]['user_birthday'])) : '';
+    $poster_birthday = ($poster_id != GUEST_UID && $postrow[$i]['user_birthday'] != '0000-00-00') ? date('md', strtotime($postrow[$i]['user_birthday'])) : '';
     $post_date = bb_date($postrow[$i]['post_time'], $bb_cfg['post_date_format']);
     $max_post_time = max($max_post_time, $postrow[$i]['post_time']);
     $poster_posts = ($poster_id != GUEST_UID) ? $postrow[$i]['user_posts'] : '';