diff --git a/classes/text_filter.php b/classes/text_filter.php
index 095ee3b..9a167e3 100644
--- a/classes/text_filter.php
+++ b/classes/text_filter.php
@@ -2379,7 +2379,7 @@ function ($matches) use ($now) {
 
         // Substitutions.
 
-        $u = $USER;
+        $u = clone $USER;
         if (!isloggedin() || isguestuser()) {
             $u->firstname = get_string('defaultfirstname', 'filter_filtercodes');
             $u->lastname = get_string('defaultsurname', 'filter_filtercodes');