diff --git a/package.json b/package.json
index c6071667..8b73d50c 100644
--- a/package.json
+++ b/package.json
@@ -52,5 +52,5 @@
     "staged": "lint-staged",
     "test": "./node_modules/.bin/jest"
   },
-  "version": "4.4.0"
+  "version": "4.4.1"
 }
diff --git a/src/server/proxyEvent.js b/src/server/proxyEvent.js
index 70b7c2d0..e910223f 100644
--- a/src/server/proxyEvent.js
+++ b/src/server/proxyEvent.js
@@ -4,10 +4,15 @@ const handleRequestResponse = require('./handleRequestResponse');
 const http = require('http');
 const url = require('url');
 
+const cleanHeaders = (headers) =>
+  Object.keys(headers)
+    .filter((header) => typeof headers[header] !== 'undefined')
+    .reduce((result, header) => ({ ...result, [header]: headers[header] }), {});
+
 const proxyEvent = (event, socketPath) =>
   new Promise((resolve) => {
     const requestOptions = {
-      headers: event.headers,
+      headers: cleanHeaders(event.headers),
       method: event.httpMethod,
       path: url.format({ pathname: event.path, query: event.queryStringParameters }),
       socketPath,
diff --git a/tests/server.test.js b/tests/server.test.js
index 06ab27dc..46a9cb94 100644
--- a/tests/server.test.js
+++ b/tests/server.test.js
@@ -41,3 +41,17 @@ test('basic test', async () => {
   await expect(response.headers['content-length']).toEqual('12');
   await expect(response.headers['content-type']).toEqual('text/html; charset=utf-8');
 });
+
+test('iframe sends undefined cookie', async () => {
+  const app = express();
+  const noCookieEvent = { ...event };
+
+  noCookieEvent.headers.cookie = undefined;
+  noCookieEvent.headers.Cookie = undefined;
+
+  app.get('/', (req, res) => res.send('Hello World!'));
+
+  const response = await lambdaServer(app, true)(noCookieEvent);
+
+  await expect(response.body).toEqual('SGVsbG8gV29ybGQh');
+});