diff --git a/package.json b/package.json
index 6bfd08b6..42a65bc3 100644
--- a/package.json
+++ b/package.json
@@ -23,7 +23,6 @@
     "url": "https://github.com/streamich/memfs.git"
   },
   "dependencies": {
-    "fast-extend": "1.0.2",
     "fs-monkey": "0.3.3"
   },
   "devDependencies": {
diff --git a/src/volume.ts b/src/volume.ts
index df9a50b3..d86014e4 100644
--- a/src/volume.ts
+++ b/src/volume.ts
@@ -12,7 +12,6 @@ import { constants } from './constants';
 import { EventEmitter } from 'events';
 import { TEncodingExtended, TDataOut, assertEncoding, strToEncoding, ENCODING_UTF8 } from './encoding';
 import * as errors from './internal/errors';
-const { extend } = require('fast-extend');
 import util = require('util');
 import createPromisesApi from './promises';
 
@@ -215,10 +214,10 @@ function getOptions<T extends IOptions>(defaults: T, options?: T | string): T {
     const tipeof = typeof options;
     switch (tipeof) {
       case 'string':
-        opts = extend({}, defaults, { encoding: options as string });
+        opts = Object.assign({}, defaults, { encoding: options as string });
         break;
       case 'object':
-        opts = extend({}, defaults, options);
+        opts = Object.assign({}, defaults, options);
         break;
       default:
         throw TypeError(ERRSTR_OPTS(tipeof));
@@ -339,8 +338,8 @@ const mkdirDefaults: IMkdirOptions = {
   recursive: false,
 };
 const getMkdirOptions = (options): IMkdirOptions => {
-  if (typeof options === 'number') return extend({}, mkdirDefaults, { mode: options });
-  return extend({}, mkdirDefaults, options);
+  if (typeof options === 'number') return Object.assign({}, mkdirDefaults, { mode: options });
+  return Object.assign({}, mkdirDefaults, options);
 };
 
 // Options for `fs.rmdir` and `fs.rmdirSync`
@@ -351,7 +350,7 @@ const rmdirDefaults: IRmdirOptions = {
   recursive: false,
 };
 const getRmdirOptions = (options): IRmdirOptions => {
-  return extend({}, rmdirDefaults, options);
+  return Object.assign({}, rmdirDefaults, options);
 };
 
 // Options for `fs.readdir` and `fs.readdirSync`
@@ -372,7 +371,7 @@ export interface IStatOptions {
 const statDefaults: IStatOptions = {
   bigint: false,
 };
-const getStatOptions: (options?: any) => IStatOptions = (options = {}) => extend({}, statDefaults, options);
+const getStatOptions: (options?: any) => IStatOptions = (options = {}) => Object.assign({}, statDefaults, options);
 const getStatOptsAndCb: (options: any, callback?: TCallback<Stats>) => [IStatOptions, TCallback<Stats>] = (
   options,
   callback?,
@@ -579,7 +578,7 @@ export class Volume {
   }
 
   constructor(props = {}) {
-    this.props = extend({ Node, Link, File }, props);
+    this.props = Object.assign({ Node, Link, File }, props);
 
     const root = this.createLink();
     root.setNode(this.createNode(true));
@@ -2228,7 +2227,7 @@ function FsReadStream(vol, path, options) {
   this._vol = vol;
 
   // a little bit bigger buffer and water marks by default
-  options = extend({}, getOptions(options, {}));
+  options = Object.assign({}, getOptions(options, {}));
   if (options.highWaterMark === undefined) options.highWaterMark = 64 * 1024;
 
   Readable.call(this, options);
@@ -2390,7 +2389,7 @@ function FsWriteStream(vol, path, options) {
   if (!(this instanceof FsWriteStream)) return new (FsWriteStream as any)(vol, path, options);
 
   this._vol = vol;
-  options = extend({}, getOptions(options, {}));
+  options = Object.assign({}, getOptions(options, {}));
 
   Writable.call(this, options);
 
diff --git a/tsconfig.json b/tsconfig.json
index 80711f9d..96c4d60d 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,7 +1,7 @@
 {
   "compilerOptions": {
     "target": "es5",
-    "lib": ["es5", "dom", "es2015.promise"],
+    "lib": ["ES2017", "dom"],
     "module": "commonjs",
     "removeComments": false,
     "noImplicitAny": false,
diff --git a/yarn.lock b/yarn.lock
index 33c052a5..d16ea0fd 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2183,11 +2183,6 @@ fast-deep-equal@^2.0.1:
   resolved "https://registry.yarnpkg.com/fast-deep-equal/-/fast-deep-equal-2.0.1.tgz#7b05218ddf9667bf7f370bf7fdb2cb15fdd0aa49"
   integrity sha1-ewUhjd+WZ79/Nwv3/bLLFf3Qqkk=
 
-fast-extend@1.0.2:
-  version "1.0.2"
-  resolved "https://registry.yarnpkg.com/fast-extend/-/fast-extend-1.0.2.tgz#3b8a5b09cbc8ff3d6d47eaf397398c0a643e441b"
-  integrity sha512-XXA9RmlPatkFKUzqVZAFth18R4Wo+Xug/S+C7YlYA3xrXwfPlW3dqNwOb4hvQo7wZJ2cNDYhrYuPzVOfHy5/uQ==
-
 fast-glob@^2.2.6:
   version "2.2.7"
   resolved "https://registry.yarnpkg.com/fast-glob/-/fast-glob-2.2.7.tgz#6953857c3afa475fff92ee6015d52da70a4cd39d"