diff --git a/S3.php b/S3.php
index 391a1e2a..a4a49eda 100644
--- a/S3.php
+++ b/S3.php
@@ -2040,6 +2040,7 @@ public static function __getSignatureV4($aHeaders, $headers, $method='GET', $uri
 		if (strpos($uri, '?')) {
 			list ($uri, $query_str) = @explode("?", $uri);
 			parse_str($query_str, $parameters);
+			ksort($parameters); //parameters need to be in sorted order
 		}
 
 		// CanonicalRequests