--- mod/forum/lib.php	(revision 2905)
+++ mod/forum/lib.php	(working copy)
@@ -3190,7 +3190,7 @@
     echo "</td>\n";
 
     // User name
-    $fullname = fullname($post, has_capability('moodle/site:viewfullnames', $modcontext));
+    $fullname = fullname($postuser, has_capability('moodle/site:viewfullnames', $modcontext));
     echo '<td class="author">';
     echo '<a href="'.$CFG->wwwroot.'/user/view.php?id='.$post->userid.'&amp;course='.$forum->course.'">'.$fullname.'</a>';
     echo "</td>\n";