diff --git a/src/JSLikeHTMLElement.php b/src/JSLikeHTMLElement.php
index 23585ff..18fe9f7 100644
--- a/src/JSLikeHTMLElement.php
+++ b/src/JSLikeHTMLElement.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // SPDX-FileCopyrightText: 2011 Keyvan Minoukadeh - http://www.keyvan.net - keyvan@keyvan.net
 // SPDX-License-Identifier: Apache-2.0
 
diff --git a/src/Readability.php b/src/Readability.php
index 8cf7202..c0ab7e4 100644
--- a/src/Readability.php
+++ b/src/Readability.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Readability;
 
 use Masterminds\HTML5;
diff --git a/tests/ReadabilityTest.php b/tests/ReadabilityTest.php
index 21f9bf7..390f85a 100644
--- a/tests/ReadabilityTest.php
+++ b/tests/ReadabilityTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Tests\Readability;
 
 use Monolog\Handler\TestHandler;