diff --git a/src/Signature/SignatureV4.php b/src/Signature/SignatureV4.php
index 74c3940fcc..9a5e296503 100644
--- a/src/Signature/SignatureV4.php
+++ b/src/Signature/SignatureV4.php
@@ -67,7 +67,7 @@ protected function getHeaderBlacklist()
             'from'                  => true,
             'referer'               => true,
             'user-agent'            => true,
-            'X-Amz-User-Agent'      => true,
+            'x-amz-user-agent'      => true,
             'x-amzn-trace-id'       => true,
             'aws-sdk-invocation-id' => true,
             'aws-sdk-retry'         => true,