diff --git a/lib/response.php b/lib/response.php
index 9edae3603b..a75135c017 100644
--- a/lib/response.php
+++ b/lib/response.php
@@ -116,7 +116,7 @@ class OC_Response {
 			self::setStatus(self::STATUS_NOT_MODIFIED);
 			exit;
 		}
-		header('ETag: '.$etag);
+		header('ETag: "'.$etag.'"');
 	}
 
 	/**