diff --git a/src/Rest/HttpExchangeFormatter.php b/src/Rest/HttpExchangeFormatter.php
index f4cee95..d757089 100644
--- a/src/Rest/HttpExchangeFormatter.php
+++ b/src/Rest/HttpExchangeFormatter.php
@@ -11,7 +11,7 @@ class HttpExchangeFormatter
 
     private $response;
 
-    public function __construct(RequestInterface $request = null, ResponseInterface $response = null)
+    public function __construct(?RequestInterface $request = null, ?ResponseInterface $response = null)
     {
         $this->request = $request;
         $this->response = $response;
diff --git a/src/Rest/RestApiBrowser.php b/src/Rest/RestApiBrowser.php
index 60143bc..406016c 100644
--- a/src/Rest/RestApiBrowser.php
+++ b/src/Rest/RestApiBrowser.php
@@ -40,7 +40,7 @@ class RestApiBrowser
     /**
      * @param string $host
      */
-    public function __construct($host, ClientInterface $httpClient = null)
+    public function __construct($host, ?ClientInterface $httpClient = null)
     {
         $this->host = $host;
         $this->httpClient = $httpClient ?: Psr18ClientDiscovery::find();