diff --git a/jest.config.js b/jest.config.js
index 66bbe01be9..8bb2ddeeff 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -27,5 +27,5 @@ module.exports = {
   transform: {
     '^.+\\.[jt]sx?$': 'babel-jest',
   },
-  setupFiles: ['./jest/stylelint-rule-test.js', 'array-flat-polyfill'],
+  setupFiles: ['./jest/stylelint-rule-test.js'],
 };
diff --git a/packages/docusaurus-plugin-content-docs/src/sidebars.ts b/packages/docusaurus-plugin-content-docs/src/sidebars.ts
index 81018e50eb..005c095458 100644
--- a/packages/docusaurus-plugin-content-docs/src/sidebars.ts
+++ b/packages/docusaurus-plugin-content-docs/src/sidebars.ts
@@ -5,6 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import _ from 'lodash';
 import fs from 'fs-extra';
 import importFresh from 'import-fresh';
 import {
@@ -105,12 +106,12 @@ function normalizeItem(item: SidebarItemRaw): SidebarItem[] {
     ];
   }
   if (isCategoryShorthand(item)) {
-    return normalizeCategoryShorthand(item).flatMap(normalizeItem);
+    return _.flatMap(normalizeCategoryShorthand(item), normalizeItem);
   }
   switch (item.type) {
     case 'category':
       assertIsCategory(item);
-      return [{...item, items: item.items.flatMap(normalizeItem)}];
+      return [{...item, items: _.flatMap(item.items, normalizeItem)}];
     case 'link':
       assertIsLink(item);
       return [item];
@@ -133,7 +134,7 @@ function normalizeSidebar(sidebars: SidebarRaw): Sidebar {
         ? sidebar
         : normalizeCategoryShorthand(sidebar);
 
-      acc[sidebarId] = normalizedSidebar.flatMap(normalizeItem);
+      acc[sidebarId] = _.flatMap(normalizedSidebar, normalizeItem);
 
       return acc;
     },
diff --git a/packages/docusaurus/package.json b/packages/docusaurus/package.json
index e0008b4212..b66f4e55c9 100644
--- a/packages/docusaurus/package.json
+++ b/packages/docusaurus/package.json
@@ -41,7 +41,6 @@
     "@babel/runtime": "^7.7.4",
     "@docusaurus/utils": "^2.0.0-alpha.49",
     "@endiliey/static-site-generator-webpack-plugin": "^4.0.0",
-    "array-flat-polyfill": "^1.0.1",
     "babel-loader": "^8.0.6",
     "babel-plugin-dynamic-import-node": "^2.3.0",
     "cache-loader": "^4.1.0",
diff --git a/packages/docusaurus/src/index.ts b/packages/docusaurus/src/index.ts
index 4f79a8a343..543b405a3b 100644
--- a/packages/docusaurus/src/index.ts
+++ b/packages/docusaurus/src/index.ts
@@ -5,8 +5,6 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import 'array-flat-polyfill';
-
 export {build} from './commands/build';
 export {start} from './commands/start';
 export {swizzle} from './commands/swizzle';
diff --git a/yarn.lock b/yarn.lock
index 6f0f33fe72..942b385625 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3196,11 +3196,6 @@ array-find-index@^1.0.1:
   resolved "https://registry.yarnpkg.com/array-find-index/-/array-find-index-1.0.2.tgz#df010aa1287e164bbda6f9723b0a96a1ec4187a1"
   integrity sha1-3wEKoSh+Fku9pvlyOwqWoexBh6E=
 
-array-flat-polyfill@^1.0.1:
-  version "1.0.1"
-  resolved "https://registry.yarnpkg.com/array-flat-polyfill/-/array-flat-polyfill-1.0.1.tgz#1e3a4255be619dfbffbfd1d635c1cf357cd034e7"
-  integrity sha512-hfJmKupmQN0lwi0xG6FQ5U8Rd97RnIERplymOv/qpq8AoNKPPAnxJadjFA23FNWm88wykh9HmpLJUUwUtNU/iw==
-
 array-flatten@1.1.1:
   version "1.1.1"
   resolved "https://registry.yarnpkg.com/array-flatten/-/array-flatten-1.1.1.tgz#9a5f699051b1e7073328f2a008968b64ea2955d2"