diff --git a/app/javascript/mastodon/base_polyfills.js b/app/javascript/mastodon/base_polyfills.js
index 12096d902..d3ac0d510 100644
--- a/app/javascript/mastodon/base_polyfills.js
+++ b/app/javascript/mastodon/base_polyfills.js
@@ -4,7 +4,6 @@ import 'es6-symbol/implement';
 import includes from 'array-includes';
 import assign from 'object-assign';
 import values from 'object.values';
-import isNaN from 'is-nan';
 import { decode as decodeBase64 } from './utils/base64';
 import promiseFinally from 'promise.prototype.finally';
 
@@ -20,10 +19,6 @@ if (!Object.values) {
   values.shim();
 }
 
-if (!Number.isNaN) {
-  Number.isNaN = isNaN;
-}
-
 promiseFinally.shim();
 
 if (!HTMLCanvasElement.prototype.toBlob) {
diff --git a/app/javascript/mastodon/load_polyfills.js b/app/javascript/mastodon/load_polyfills.js
index f5a897f75..b2c41303a 100644
--- a/app/javascript/mastodon/load_polyfills.js
+++ b/app/javascript/mastodon/load_polyfills.js
@@ -15,7 +15,6 @@ function loadPolyfills() {
     Array.prototype.includes &&
     HTMLCanvasElement.prototype.toBlob &&
     window.Intl &&
-    Number.isNaN &&
     Object.assign &&
     Object.values &&
     window.Symbol &&
diff --git a/package.json b/package.json
index 247fe66ab..ed9f72e8c 100644
--- a/package.json
+++ b/package.json
@@ -70,7 +70,6 @@
     "intl": "^1.2.5",
     "intl-messageformat": "^2.2.0",
     "intl-relativeformat": "^6.4.3",
-    "is-nan": "^1.3.2",
     "js-yaml": "^4.1.0",
     "jsdom": "^21.1.1",
     "lodash": "^4.17.21",
diff --git a/yarn.lock b/yarn.lock
index d09efa23b..3d6379246 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -6108,14 +6108,6 @@ is-module@^1.0.0:
   resolved "https://registry.yarnpkg.com/is-module/-/is-module-1.0.0.tgz#3258fb69f78c14d5b815d664336b4cffb6441591"
   integrity sha1-Mlj7afeMFNW4FdZkM2tM/7ZEFZE=
 
-is-nan@^1.3.2:
-  version "1.3.2"
-  resolved "https://registry.yarnpkg.com/is-nan/-/is-nan-1.3.2.tgz#043a54adea31748b55b6cd4e09aadafa69bd9e1d"
-  integrity sha512-E+zBKpQ2t6MEo1VsonYmluk9NxGrbzpeeLC2xIViuO2EjU2xsXsBPwTr3Ykv9l08UYEVEdWeRZNouaZqF6RN0w==
-  dependencies:
-    call-bind "^1.0.0"
-    define-properties "^1.1.3"
-
 is-negative-zero@^2.0.2:
   version "2.0.2"
   resolved "https://registry.yarnpkg.com/is-negative-zero/-/is-negative-zero-2.0.2.tgz#7bf6f03a28003b8b3965de3ac26f664d765f3150"