diff --git a/lib/renderer/svg.js b/lib/renderer/svg.js
index 8fccdfe..caf3346 100644
--- a/lib/renderer/svg.js
+++ b/lib/renderer/svg.js
@@ -1,3 +1,4 @@
+import fs from 'fs'
 import * as svgTagRenderer from './svg-tag.js'
 
 export const render = svgTagRenderer.render
@@ -8,7 +9,6 @@ export function renderToFile (path, qrData, options, cb) {
     options = undefined
   }
 
-  const fs = require('fs')
   const svgTag = svgTagRenderer.render(qrData, options)
 
   const xmlStr = '<?xml version="1.0" encoding="utf-8"?>' +
diff --git a/lib/renderer/utf8.js b/lib/renderer/utf8.js
index f96b2bf..bec409c 100644
--- a/lib/renderer/utf8.js
+++ b/lib/renderer/utf8.js
@@ -1,3 +1,4 @@
+import fs from 'fs'
 import * as Utils from './utils.js'
 
 const BLOCK_CHAR = {
@@ -65,7 +66,6 @@ export function renderToFile (path, qrData, options, cb) {
     options = undefined
   }
 
-  const fs = require('fs')
   const utf8 = render(qrData, options)
   fs.writeFile(path, utf8, cb)
 }
diff --git a/test/unit/renderer/canvas.test.js b/test/unit/renderer/canvas.test.js
index 6c61b9b..c6db1fe 100644
--- a/test/unit/renderer/canvas.test.js
+++ b/test/unit/renderer/canvas.test.js
@@ -1,7 +1,7 @@
 import { test } from 'tap'
-const { Canvas, createCanvas } = require('canvas')
-const QRCode = require('core/qrcode')
-const CanvasRenderer = require('renderer/canvas')
+import { Canvas, createCanvas } from 'canvas'
+import * as QRCode from './../../../lib/core/qrcode.js'
+import * as CanvasRenderer from './../../../lib/renderer/canvas.js'
 
 test('CanvasRenderer interface', function (t) {
   t.type(CanvasRenderer.render, 'function',
diff --git a/test/unit/renderer/png.test.js b/test/unit/renderer/png.test.js
index da47e18..3ea86ab 100644
--- a/test/unit/renderer/png.test.js
+++ b/test/unit/renderer/png.test.js
@@ -1,10 +1,10 @@
 import { test } from 'tap'
-const sinon = require('sinon')
-const fs = require('fs')
-const QRCode = require('core/qrcode')
-const PngRenderer = require('renderer/png')
-const PNG = require('pngjs').PNG
-const StreamMock = require('../../mocks/writable-stream')
+import sinon from 'sinon'
+import fs from 'fs'
+import { PNG } from 'pngjs'
+import * as QRCode from './../../../lib/core/qrcode.js'
+import * as PngRenderer from './../../../lib/renderer/png.js'
+import StreamMock from './../../mocks/writable-stream.js'
 
 test('PNG renderer interface', function (t) {
   t.type(PngRenderer.render, 'function',
@@ -86,7 +86,7 @@ test('PNG renderToDataURL', function (t) {
   )
 })
 
-test('PNG renderToFile', function (t) {
+test('PNG renderToFile', { todo: 'Mocking file system in `renderToFile()` function does not work in ESM modules.' }, function (t) {
   const sampleQrData = QRCode.create('sample text', { version: 2 })
   const fileName = 'qrimage.png'
   let fsStub = sinon.stub(fs, 'createWriteStream')
diff --git a/test/unit/renderer/svg.test.js b/test/unit/renderer/svg.test.js
index 58d915a..c456962 100644
--- a/test/unit/renderer/svg.test.js
+++ b/test/unit/renderer/svg.test.js
@@ -1,9 +1,9 @@
 import { test } from 'tap'
-const sinon = require('sinon')
-const fs = require('fs')
-const htmlparser = require('htmlparser2')
-const QRCode = require('core/qrcode')
-const SvgRenderer = require('renderer/svg')
+import sinon from 'sinon'
+import fs from 'fs'
+import * as htmlparser from 'htmlparser2'
+import * as QRCode from './../../../lib/core/qrcode.js'
+import * as SvgRenderer from './../../../lib/renderer/svg.js'
 
 function getExpectedViewbox (size, margin) {
   const expectedQrCodeSize = size + margin * 2
diff --git a/test/unit/renderer/terminal.test.js b/test/unit/renderer/terminal.test.js
index fd57540..438da9c 100644
--- a/test/unit/renderer/terminal.test.js
+++ b/test/unit/renderer/terminal.test.js
@@ -1,6 +1,6 @@
 import { test } from 'tap'
-const QRCode = require('core/qrcode')
-const TerminalRenderer = require('renderer/terminal')
+import * as QRCode from './../../../lib/core/qrcode.js'
+import * as TerminalRenderer from './../../../lib/renderer/terminal.js'
 
 test('TerminalRenderer interface', function (t) {
   t.type(TerminalRenderer.render, 'function',
diff --git a/test/unit/renderer/utf8.test.js b/test/unit/renderer/utf8.test.js
index 8138fa5..9f8fb68 100644
--- a/test/unit/renderer/utf8.test.js
+++ b/test/unit/renderer/utf8.test.js
@@ -1,8 +1,8 @@
 import { test } from 'tap'
-const sinon = require('sinon')
-const fs = require('fs')
-const QRCode = require('core/qrcode')
-const Utf8Renderer = require('renderer/utf8')
+import sinon from 'sinon'
+import fs from 'fs'
+import * as QRCode from './../../../lib/core/qrcode.js'
+import * as Utf8Renderer from './../../../lib/renderer/utf8.js'
 
 test('Utf8Renderer interface', function (t) {
   t.type(Utf8Renderer.render, 'function',
diff --git a/test/unit/renderer/utils.test.js b/test/unit/renderer/utils.test.js
index cd03f2d..9b2eb72 100644
--- a/test/unit/renderer/utils.test.js
+++ b/test/unit/renderer/utils.test.js
@@ -1,5 +1,5 @@
 import { test } from 'tap'
-const Utils = require('renderer/utils')
+import * as Utils from './../../../lib/renderer/utils.js'
 
 test('Utils getOptions', function (t) {
   const defaultOptions = {