diff --git a/spec/normalizeStatusCode.spec.js b/spec/normalizeStatusCode.spec.js
index d2720db..85e0cca 100644
--- a/spec/normalizeStatusCode.spec.js
+++ b/spec/normalizeStatusCode.spec.js
@@ -6,7 +6,11 @@ const normalizeStatusCode = require('../src/normalizeStatusCode');
 describe('normalizeStatusCode', () => {
   it('returns run callback if configured', () => {
     expect(
-      normalizeStatusCode({status_code: 500})
+      normalizeStatusCode({status_code: 500, headersSent: true})
     ).toBe(500);
   });
+
+  it('returns 499 if headers are not sent', () => {
+    expect(normalizeStatusCode({statusCode: 200, headersSent: false})).toBe(499);
+  });
 });
diff --git a/src/normalizeStatusCode.js b/src/normalizeStatusCode.js
index 545bf2f..7c11c5c 100644
--- a/src/normalizeStatusCode.js
+++ b/src/normalizeStatusCode.js
@@ -1,5 +1,11 @@
 'use strict';
 
+const CLIENT_CLOSED_REQUEST_CODE = 499;
+
 module.exports = function(res) {
-  return res.status_code || res.statusCode;
+  if (res.headersSent) {
+    return res.status_code || res.statusCode;
+  } else {
+    return CLIENT_CLOSED_REQUEST_CODE;
+  }
 };