Error in phpBB 3.2.1

[Leinad4Mind]

[phpBB Debug] PHP Notice: in file /forum/includes/functions.php on line 4638: [phpBB Debug] PHP Notice: in file [ROOT]/includes/functions.php on line 4638: Undefined variable: phpbb_root_path

FILE: [ROOT]/includes/functions.php LINE: 4638 CALL: stk_msg_handler()

FILE: [ROOT]/stk/index.php LINE: 424 CALL: page_footer()

EDIT: I've edited my code and forgot to instanciate the variable. My bad