diff --git a/src/ResourceServer.php b/src/ResourceServer.php
index 245cb4e2..697afdf4 100644
--- a/src/ResourceServer.php
+++ b/src/ResourceServer.php
@@ -138,7 +138,7 @@ class ResourceServer extends AbstractServer
      */
     public function determineAccessToken($headerOnly = false)
     {
-        if ($this->getRequest()->headers->get('Authorization') !== null) {
+        if (!empty($this->getRequest()->headers->get('Authorization'))) {
             $accessToken = $this->getTokenType()->determineAccessTokenInHeader($this->getRequest());
         } elseif ($headerOnly === false && (! $this->getTokenType() instanceof MAC)) {
             $accessToken = ($this->getRequest()->server->get('REQUEST_METHOD') === 'GET')