diff --git a/tests/Dotenv/Repository/RepositoryTest.php b/tests/Dotenv/Repository/RepositoryTest.php
index ce296dc6..6c8b70e5 100644
--- a/tests/Dotenv/Repository/RepositoryTest.php
+++ b/tests/Dotenv/Repository/RepositoryTest.php
@@ -66,8 +66,7 @@ private function key()
     {
         $keyVal = $this->keyVal();
 
-        /** @var string */
-        return \key($keyVal);
+        return (string) \key($keyVal);
     }
 
     /**