diff --git a/resources/skins.vector.js/legacyMessageBoxStyles.js b/resources/skins.vector.js/legacyMessageBoxStyles.js
deleted file mode 100644
index 5e045c2e9..000000000
--- a/resources/skins.vector.js/legacyMessageBoxStyles.js
+++ /dev/null
@@ -1,11 +0,0 @@
-/**
- * Checks if the page is using legacy message box styles
- */
-module.exports = function () {
-	mw.requestIdleCallback( () => {
-		if ( document.querySelectorAll( '.mw-message-box:not(.cdx-message)' ).length ) {
-			mw.log.warn( `[T360668] A message box on this page is not using standard markup.
-See https://doc.wikimedia.org/codex/latest/components/demos/message.html#markup-structure for more information.` );
-		}
-	} );
-};
diff --git a/resources/skins.vector.js/skin.js b/resources/skins.vector.js/skin.js
index f0ef56869..3375b94f0 100644
--- a/resources/skins.vector.js/skin.js
+++ b/resources/skins.vector.js/skin.js
@@ -12,7 +12,6 @@ const languageButton = require( './languageButton.js' ),
 	setupIntersectionObservers = require( './setupIntersectionObservers.js' ),
 	menuTabs = require( './menuTabs.js' ),
 	userPreferences = require( './userPreferences.js' ),
-	legacyMessageBoxStyles = require( './legacyMessageBoxStyles.js' ),
 	{ isNightModeGadgetEnabled, disableNightModeForGadget, alterExclusionMessage, removeBetaNotice } = require( './disableNightModeIfGadget.js' ),
 	teleportTarget = /** @type {HTMLElement} */require( /** @type {string} */ ( 'mediawiki.page.ready' ) ).teleportTarget;
 
@@ -114,7 +113,6 @@ function main( window ) {
  */
 function init( window ) {
 	const now = mw.now();
-	legacyMessageBoxStyles();
 	// This is the earliest time we can run JS for users (and bucket anonymous
 	// users for A/B tests).
 	// Where the browser supports it, for a 10% sample of users
diff --git a/skin.json b/skin.json
index b022c115a..73581fe87 100644
--- a/skin.json
+++ b/skin.json
@@ -262,7 +262,6 @@
 				"content-links": true,
 				"content-links-external": false,
 				"interface": true,
-				"interface-message-box": true,
 				"interface-category": true,
 				"content-tables": true,
 				"i18n-ordered-lists": true,
@@ -285,7 +284,6 @@
 				"interface-category": true,
 				"interface-edit-section-links": true,
 				"interface-indicators": false,
-				"interface-message-box": false,
 				"interface-site-notice": false,
 				"interface-subtitle": false,
 				"interface-user-message": true,
@@ -396,15 +394,11 @@
 		},
 		"skins.vector.js": {
 			"class": "MediaWiki\\ResourceLoader\\SkinModule",
-			"features": [
-				"interface-message-box"
-			],
 			"styles": [
 				"resources/skins.vector.js/index.less"
 			],
 			"packageFiles": [
 				"resources/skins.vector.js/skin.js",
-				"resources/skins.vector.js/legacyMessageBoxStyles.js",
 				"resources/skins.vector.js/setupIntersectionObservers.js",
 				"resources/skins.vector.js/searchToggle.js",
 				"resources/skins.vector.js/stickyHeader.js",