diff --git a/docs/EXPRESS_SERVER.MD b/docs/EXPRESS_SERVER.MD
index fbec6267..2524455c 100644
--- a/docs/EXPRESS_SERVER.MD
+++ b/docs/EXPRESS_SERVER.MD
@@ -24,7 +24,7 @@ const hasBotResult = (result) => {
 // create middleware
 const middlewareDetect = (req, res, next) => {
   const useragent = req.headers['user-agent']; 
-  const clientHintsData = clientHints.parse(res.headers);
+  const clientHintsData = clientHints.parse(req.headers);
 
   req.useragent = useragent;
   req.device = deviceDetector.detect(useragent, clientHintsData);
@@ -46,4 +46,4 @@ app.get('/detect', (req, res) => {
 app.listen(port, () => {
   console.log('server listen port %s', port);
 })
-```
\ No newline at end of file
+```