diff --git a/Lescript.php b/Lescript.php
index b81d01f..9ffad9f 100644
--- a/Lescript.php
+++ b/Lescript.php
@@ -31,7 +31,7 @@ class Lescript
     protected $urlNewNonce = '';
     protected $urlNewOrder = '';
 
-    public function __construct($certificatesDir, $webRootDir, $logger = null, ClientInterface $client = null)
+    public function __construct($certificatesDir, $webRootDir, $logger = null, ClientInterface|null $client = null)
     {
         $this->certificatesDir = $certificatesDir;
         $this->webRootDir = $webRootDir;