diff --git a/S3.php b/S3.php
index 88af763..cfa09ed 100644
--- a/S3.php
+++ b/S3.php
@@ -2004,7 +2004,7 @@ public static function __getSignatureV4($amzHeaders, $headers, $method, $uri, $p
 
 		// CanonicalHeaders
 		foreach ($headers as $k => $v)
-			$combinedHeaders[strtolower($k)] = trim($v);
+			if (!empty($v)) $combinedHeaders[strtolower($k)] = trim($v);
 		foreach ($amzHeaders as $k => $v) 
 			$combinedHeaders[strtolower($k)] = trim($v);
 		uksort($combinedHeaders, array('S3', '__sortMetaHeadersCmp'));