diff --git a/tests/UnusedCodeTest.php b/tests/UnusedCodeTest.php
index 328e26da690..36e30901f4b 100644
--- a/tests/UnusedCodeTest.php
+++ b/tests/UnusedCodeTest.php
@@ -187,7 +187,7 @@ private function foo() : void {}
             'everythingUsed' => [
                 '<?php
                     interface I {
-                        public function foo();
+                        public function foo() : void;
                     }
                     class B implements I {
                         public function foo() : void {}