diff --git a/__tests__/integration.js b/__tests__/integration.js
index 2c112ce4..de33044d 100644
--- a/__tests__/integration.js
+++ b/__tests__/integration.js
@@ -6,7 +6,7 @@ const app = require('../examples/basic-starter/app')
 
 const server = awsServerlessExpress.createServer(app)
 const lambdaFunction = {
-  handler: (event, context, resolutionMode, callback) => awsServerlessExpress.proxy(server, event, context, resolutionMode, callback)
+  handler: (event, context, resolutionMode, callback, _server) => awsServerlessExpress.proxy(_server || server, event, context, resolutionMode, callback)
 }
 
 function clone (json) {
@@ -96,6 +96,7 @@ describe('integration tests', () => {
       succeed
     })
   })
+
   test('GET JSON collection', (done) => {
     const succeed = response => {
       delete response.headers.date
@@ -199,6 +200,27 @@ describe('integration tests', () => {
       .promise.then(succeed)
   })
 
+  test('GET JSON single (resolutionMode = PROMISE; new server)', (done) => {
+    const succeed = response => {
+      delete response.headers.date
+      expect(response).toEqual(makeResponse({
+        'body': '{"id":1,"name":"Joe"}',
+        'headers': {
+          'content-length': '21',
+          'etag': 'W/"15-rRboW+j/yFKqYqV6yklp53+fANQ"'
+        }
+      }))
+      newServer.close()
+      done()
+    }
+    const newServer = awsServerlessExpress.createServer(app)
+    lambdaFunction.handler(makeEvent({
+      path: '/users/1',
+      httpMethod: 'GET'
+    }), {}, 'PROMISE', null, newServer)
+      .promise.then(succeed)
+  })
+
   test('GET JSON single 404', (done) => {
     const succeed = response => {
       delete response.headers.date
diff --git a/__tests__/unit.js b/__tests__/unit.js
index 6462d1df..55f94ade 100644
--- a/__tests__/unit.js
+++ b/__tests__/unit.js
@@ -72,6 +72,7 @@ test('mapApiGatewayEventToHttpRequest: with headers', () => {
     path: '/foo',
     headers: {
       'x-foo': 'foo',
+      'Content-Length': Buffer.byteLength('Hello serverless!'),
       'x-apigateway-event': encodeURIComponent(JSON.stringify(r.eventClone)),
       'x-apigateway-context': encodeURIComponent(JSON.stringify(r.context))
     },
@@ -86,6 +87,7 @@ test('mapApiGatewayEventToHttpRequest: without headers', () => {
     method: 'GET',
     path: '/foo',
     headers: {
+      'Content-Length': Buffer.byteLength('Hello serverless!'),
       'x-apigateway-event': encodeURIComponent(JSON.stringify(r.eventClone)),
       'x-apigateway-context': encodeURIComponent(JSON.stringify(r.context))
     },
diff --git a/package.json b/package.json
index 5827ea25..7acd512a 100644
--- a/package.json
+++ b/package.json
@@ -46,6 +46,7 @@
         "path": "@semantic-release/git",
         "assets": [
           "package.json",
+          "package-lock.json",
           "CHANGELOG.md",
           "dist/**/*.{js|css}"
         ],
@@ -104,7 +105,7 @@
   },
   "scripts": {
     "test": "jest",
-    "test-watch": "jest --watch",
+    "test:watch": "jest --watch",
     "coverage": "jest --coverage",
     "cz": "git-cz",
     "release": "semantic-release",
diff --git a/src/index.js b/src/index.js
index 98fc2169..3db57d31 100644
--- a/src/index.js
+++ b/src/index.js
@@ -21,6 +21,13 @@ const isType = require('type-is')
 function getPathWithQueryStringParams (event) {
   return url.format({ pathname: event.path, query: event.queryStringParameters })
 }
+function getEventBody (event) {
+  return Buffer.from(event.body, event.isBase64Encoded ? 'base64' : 'utf8')
+}
+
+function clone (json) {
+  return JSON.parse(JSON.stringify(json))
+}
 
 function getContentType (params) {
   // only compare mime type; ignore encoding part
@@ -32,11 +39,18 @@ function isContentTypeBinaryMimeType (params) {
 }
 
 function mapApiGatewayEventToHttpRequest (event, context, socketPath) {
-  const headers = event.headers || {} // NOTE: Mutating event.headers; prefer deep clone of event.headers
-  const eventWithoutBody = Object.assign({}, event)
-  delete eventWithoutBody.body
+  const headers = Object.assign({}, event.headers)
 
-  headers['x-apigateway-event'] = encodeURIComponent(JSON.stringify(eventWithoutBody))
+  // NOTE: API Gateway is not setting Content-Length header on requests even when they have a body
+  if (event.body && !headers['Content-Length']) {
+    const body = getEventBody(event)
+    headers['Content-Length'] = Buffer.byteLength(body)
+  }
+
+  const clonedEventWithoutBody = clone(event)
+  delete clonedEventWithoutBody.body
+
+  headers['x-apigateway-event'] = encodeURIComponent(JSON.stringify(clonedEventWithoutBody))
   headers['x-apigateway-context'] = encodeURIComponent(JSON.stringify(context))
 
   return {
@@ -121,11 +135,9 @@ function forwardRequestToNodeServer (server, event, context, resolver) {
     const requestOptions = mapApiGatewayEventToHttpRequest(event, context, getSocketPath(server._socketPathSuffix))
     const req = http.request(requestOptions, (response) => forwardResponseToApiGateway(server, response, resolver))
     if (event.body) {
-      if (event.isBase64Encoded) {
-        event.body = Buffer.from(event.body, 'base64')
-      }
+      const body = getEventBody(event)
 
-      req.write(event.body)
+      req.write(body)
     }
 
     req.on('error', (error) => forwardConnectionErrorResponseToApiGateway(error, resolver))