diff --git a/src/Codeception/Lib/Connector/Yii2.php b/src/Codeception/Lib/Connector/Yii2.php
index fadb35e..d18a3a3 100644
--- a/src/Codeception/Lib/Connector/Yii2.php
+++ b/src/Codeception/Lib/Connector/Yii2.php
@@ -480,7 +480,7 @@ protected function mockMailer(array $config)
         return $config;
     }
 
-    public function restart()
+    public function restart(): void
     {
         parent::restart();
         $this->resetApplication();