diff --git a/tests/di.php b/tests/di.php
index d464735..8542826 100644
--- a/tests/di.php
+++ b/tests/di.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 use Aura\Html\HelperLocatorFactory;
 use Aura\Session\SessionFactory;