diff --git a/index.js b/index.js
index 1719726..e8f582b 100644
--- a/index.js
+++ b/index.js
@@ -1,4 +1,4 @@
-/* global fetch, Request */
+/* global fetch, Headers */
 require('isomorphic-fetch')
 
 function Client (options) {
@@ -9,12 +9,6 @@ function Client (options) {
   self.options = options
   self.url = options.url
 
-  // Request instance that is used for `fetch`ing
-  self.request = options.request instanceof Request
-    ? options.request
-    : new Request(self.url, options.request || { method: 'POST' })
-  self.request.headers.append('content-type', 'application/json')
-
   // A stack of registered listeners
   self.listeners = []
 }
@@ -32,17 +26,23 @@ var proto = Client.prototype
 proto.query = function (query, variables, beforeRequest) {
   var self = this
 
-  self.request.body = JSON.stringify({
+  var req = self.options.request || {}
+  req.method || (req.method = 'POST')
+  if (!req.headers) {
+    req.headers = new Headers()
+    req.headers.set('content-type', 'application/json')
+  }
+  req.body = JSON.stringify({
     query: query,
     variables: variables
   })
 
   // 'beforeRequest' is a top priority per-query hook, it should forcibly
   // override response even from other hooks.
-  var result = beforeRequest && beforeRequest(self.request)
+  var result = beforeRequest && beforeRequest(req)
 
   if (typeof result === 'undefined') {
-    result = self.emit('request', self.request)
+    result = self.emit('request', req)
 
     // No 'response' hook here, reserve it for real responses only.
 
@@ -56,8 +56,7 @@ proto.query = function (query, variables, beforeRequest) {
   if (typeof result !== 'undefined') {
     result = Promise.resolve(result)
   }
-
-  return result || self.fetch(self.request)
+  return result || self.fetch(req)
 }
 
 /**
@@ -68,7 +67,7 @@ proto.query = function (query, variables, beforeRequest) {
 proto.fetch = function (req) {
   var self = this
 
-  return fetch(req).then(function (res) {
+  return fetch(self.url, req).then(function (res) {
     // 'response' hook can redefine `res`
     var _res = self.emit('response', res)
     if (typeof _res !== 'undefined') res = _res
diff --git a/test/specs.js b/test/specs.js
index 4b85af7..4b40c3e 100644
--- a/test/specs.js
+++ b/test/specs.js
@@ -1,5 +1,5 @@
 /* eslint-env mocha */
-/* global Request */
+/* global Headers */
 const { expect } = require('chai')
 const { Client } = require('..')
 const server = require('./lib/server')
@@ -75,14 +75,21 @@ describe('GraphQL client', () => {
       .query('{}')
   })
 
-  it('should redefine `Request` instance before querying', (done) => {
-    const request = new Request(url)
-    request.headers.set('content-length', 3)
+  it('should modify request before querying', (done) => {
+    const headers = new Headers()
+    headers.set('content-length', 3)
+
+    const request = {
+      method: 'GET',
+      credentials: 'include',
+      headers
+    }
 
     const client = new Client({ url, request })
 
     client.on('request', (req) => {
       expect(req.method).to.equal('GET')
+      expect(req.credentials).to.equal('include')
       expect(req.headers.get('content-type')).to.be.falsy
       expect(req.headers.get('content-length')).to.equal(3)
       done()