diff --git a/.php-cs-fixer.php b/.php-cs-fixer.php
index 1dab3c0..7d3eeb4 100644
--- a/.php-cs-fixer.php
+++ b/.php-cs-fixer.php
@@ -1,4 +1,6 @@
 <?php
+
+declare(strict_types=1);
 /*
  * This document has been generated with
  * https://mlocati.github.io/php-cs-fixer-configurator/#version:3.59.3|configurator
@@ -11,6 +13,8 @@
     ->setRules([
         '@PER-CS' => true,
         '@PER-CS:risky' => true,
+        // Force strict types declaration in all files. Requires PHP >= 7.0.
+        'declare_strict_types' => true,
         // Unused `use` statements must be removed.
         'no_unused_imports' => true,
         // Multi-line arrays, arguments list, parameters list and `match` expressions must have a trailing comma.