diff --git a/src/Message/Response.php b/src/Message/Response.php
index a94e1e71..8ab3a196 100644
--- a/src/Message/Response.php
+++ b/src/Message/Response.php
@@ -388,6 +388,10 @@ public function getRequestId()
     {
         if (isset($this->headers['Request-Id'])) {
             return $this->headers['Request-Id'][0];
+        } else {
+            if (isset($this->headers[strtolower('Request-Id')])) {
+                return $this->headers[strtolower('Request-Id')][0];
+            }
         }
 
         return null;