diff --git a/lib/middlewares/pre_compressed.js b/lib/middlewares/pre_compressed.js
index 89140db..a9dfbd2 100644
--- a/lib/middlewares/pre_compressed.js
+++ b/lib/middlewares/pre_compressed.js
@@ -31,7 +31,7 @@ module.exports = function(app) {
 
     if (!vary) {
       res.setHeader('Vary', 'Accept-Encoding');
-    } else if (!~vary.indexOf('Accept-Encoding')) {
+    } else if (!vary.includes('Accept-Encoding')) {
       res.setHeader('Vary', vary + ', Accept-Encoding');
     }