diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index bb0edc4..3fc0437 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        php: [ '7.4', '8.0', '8.1', '8.2' ]
+        php: [ '7.4', '8.0', '8.1', '8.2', '8.3', '8.4' ]
         stability: [ prefer-stable ]
 
     name: PHP ${{ matrix.php }} - ${{ matrix.stability }}
diff --git a/src/MessageBird/Client.php b/src/MessageBird/Client.php
index ab84987..cc14b6e 100644
--- a/src/MessageBird/Client.php
+++ b/src/MessageBird/Client.php
@@ -147,7 +147,7 @@ class Client
      */
     protected $numbersAPIClient;
 
-    public function __construct(?string $accessKey = null, Common\HttpClient $httpClient = null, array $config = [])
+    public function __construct(?string $accessKey = null, ?Common\HttpClient $httpClient = null, array $config = [])
     {
         if ($httpClient === null) {
             $this->conversationsAPIHttpClient = new Common\HttpClient(