diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index 928fda435d5..d9f28beff99 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -3719,7 +3719,7 @@ function forum_print_discussion_header(&$post, $forum, $group=-1, $datestring=""
     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";