diff --git a/lib/sessionlib.php b/lib/sessionlib.php
index 8e64d6daa32..37225b7b7a3 100644
--- a/lib/sessionlib.php
+++ b/lib/sessionlib.php
@@ -1033,7 +1033,7 @@ function get_moodle_cookie() {
  * @return void
  */
 function session_set_user($user) {
-    $_SESSION['USER'] = $user;
+    $_SESSION['USER'] = clone $user;
     unset($_SESSION['USER']->description); // conserve memory
     if (!isset($_SESSION['USER']->access)) {
         // check enrolments and load caps only once