diff --git a/lib/AppInfo/Application.php b/lib/AppInfo/Application.php
index 5ca54e458..af92bc5f1 100644
--- a/lib/AppInfo/Application.php
+++ b/lib/AppInfo/Application.php
@@ -60,7 +60,7 @@
 use Psr\Log\LoggerInterface;
 
 class Application extends App implements IBootstrap {
-	public const APP_ID = 'groupfolders';
+	public const string APP_ID = 'groupfolders';
 
 	public function __construct(array $urlParams = []) {
 		parent::__construct(self::APP_ID, $urlParams);