diff --git a/src/Composer/Downloader/TransportException.php b/src/Composer/Downloader/TransportException.php
index 5ab5ca6f3..a30842e1e 100644
--- a/src/Composer/Downloader/TransportException.php
+++ b/src/Composer/Downloader/TransportException.php
@@ -26,7 +26,7 @@ class TransportException extends \RuntimeException
     /** @var array<mixed> */
     protected $responseInfo = [];
 
-    public function __construct(string $message = "", int $code = 400, \Throwable $previous = null)
+    public function __construct(string $message = "", int $code = 400, ?\Throwable $previous = null)
     {
         parent::__construct($message, $code, $previous);
     }