diff --git a/lib/classes/auth_plugins/StudipAuthSimpleSamlPHP.php b/lib/classes/auth_plugins/StudipAuthSimpleSamlPHP.php
index 18b7e36ff967ce00a975d08331b6e146c65cb357..a95d0cabe660bde654fc741f670bba69fff466ab 100644
--- a/lib/classes/auth_plugins/StudipAuthSimpleSamlPHP.php
+++ b/lib/classes/auth_plugins/StudipAuthSimpleSamlPHP.php
@@ -100,7 +100,7 @@ class StudipAuthSimpleSamlPHP extends StudipAuthSSO
     /**
      * Logout the user.
      */
-    public function logout()
+    public function logout(): void
     {
         $auth = new \SimpleSAML\Auth\Simple($this->sp_name);
         $auth->Logout();