diff --git a/src/MessageBird/RequestValidator.php b/src/MessageBird/RequestValidator.php
index 374f1ee..8d42fe7 100644
--- a/src/MessageBird/RequestValidator.php
+++ b/src/MessageBird/RequestValidator.php
@@ -187,8 +187,9 @@ public function validateSignature(string $signature, string $url, string $body)
      */
     public function validateRequestFromGlobals()
     {
-        $signature = $_SERVER['MessageBird-Signature-JWT'] ?? null;
-        $url = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] === 'on' ? "https" : "http") . "://$_SERVER[HTTP_HOST]$_SERVER[REQUEST_URI]";
+        $signature = $_SERVER['HTTP_MESSAGEBIRD_SIGNATURE_JWT'] ?? ($_SERVER['MessageBird-Signature-JWT'] ?? '');
+        $url = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] === 'on' ? "https" : "http") .
+            "://{$_SERVER['HTTP_HOST']}{$_SERVER['REQUEST_URI']}";
         $body = file_get_contents('php://input');
 
         return $this->validateSignature($signature, $url, $body);