diff --git a/kiri-engine/Scanner.php b/kiri-engine/Scanner.php
index 0612b11d..c26923a0 100644
--- a/kiri-engine/Scanner.php
+++ b/kiri-engine/Scanner.php
@@ -1,5 +1,8 @@
 <?php
 
+declare(strict_types=1);
+
+
 namespace Kiri;
 
 use Exception;
diff --git a/kiri-engine/ToArray.php b/kiri-engine/ToArray.php
index 29c78d73..d0df8a00 100644
--- a/kiri-engine/ToArray.php
+++ b/kiri-engine/ToArray.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Kiri;
 
 interface ToArray