diff --git a/src/IdManager.php b/src/IdManager.php
index c860e38..292e308 100644
--- a/src/IdManager.php
+++ b/src/IdManager.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace MMK2410\MyTodoList;