diff --git a/tests/phpunit/test-cdn.php b/tests/phpunit/test-cdn.php
index be2af93..927e771 100644
--- a/tests/phpunit/test-cdn.php
+++ b/tests/phpunit/test-cdn.php
@@ -28,7 +28,7 @@ public function setUp(): void {
 		update_option( 'multi_device_switcher_options', $options );
 	}
 
-	function tearDown() {
+	function tearDown(): void {
 		parent::tearDown();
 	}