diff --git a/src/index.js b/src/index.js
index 7bc2872..296932d 100644
--- a/src/index.js
+++ b/src/index.js
@@ -118,7 +118,7 @@ function main(opts) {
       let timer = metrics[httpMtricName].startTimer(labels);
       onFinished(res, () => {
         if (opts.normalizeStatusCode) {
-          labels.status_code = main.normalizeStatusCode(req, opts);
+          labels.status_code = main.normalizeStatusCode(res, opts);
         } else {
           labels.status_code = res.statusCode;
         }
diff --git a/src/normalizeStatusCode.js b/src/normalizeStatusCode.js
index 85023ed..166d676 100644
--- a/src/normalizeStatusCode.js
+++ b/src/normalizeStatusCode.js
@@ -1,22 +1,14 @@
 'use strict';
 
-module.exports = function(req, opts) {
+module.exports = function(res, opts) {
   opts = opts || {};
 
   if (opts.formatStatusCode !== undefined && !opts.formatStatusCode) {
     return req.status_code;
   }
   if (typeof opts.formatStatusCode === 'function') {
-    return opts.formatStatusCode(req, opts);
+    return opts.formatStatusCode(res, opts);
   }
 
-  // Group Status code in 1xx, 2xx, 3xx, 4xx, 5xx or other
-  const status_code = ({
-    '1': '1xx',
-    '2': '2xx',
-    '3': '3xx',
-    '4': '4xx',
-    '5': '5xx',
-  })[(req.status_code || '').substr(0,1)] || 'other';
-  return status_code;
+  return req.status_code;
 };