diff --git a/tools/regexp-generator/header.js b/tools/regexp-generator/header.mjs
similarity index 97%
rename from tools/regexp-generator/header.js
rename to tools/regexp-generator/header.mjs
index bedcf9d09a..6f2263a461 100644
--- a/tools/regexp-generator/header.js
+++ b/tools/regexp-generator/header.mjs
@@ -1,4 +1,4 @@
-module.exports = description => {
+export default description => {
     let header = `// Copyright (C) 2018 Leo Balter.  All rights reserved.
 // This code is governed by the BSD license found in the LICENSE file.
 
diff --git a/tools/regexp-generator/index.js b/tools/regexp-generator/index.mjs
similarity index 90%
rename from tools/regexp-generator/index.js
rename to tools/regexp-generator/index.mjs
index e3e816c4c6..0f664b7726 100644
--- a/tools/regexp-generator/index.js
+++ b/tools/regexp-generator/index.mjs
@@ -1,9 +1,10 @@
-const fs = require('fs');
-const rewritePattern = require('regexpu-core');
-const slugify = require('slugify');
-const filenamify = require('filenamify');
-const jsesc = require('jsesc');
-const header = require('./header');
+import filenamify from 'filenamify';
+import fs from 'node:fs';
+import jsesc from 'jsesc';
+import rewritePattern from 'regexpu-core';
+import slugify from 'slugify';
+
+import header from './header.mjs';
 
 const patterns = {
     'whitespace class escape': '\\s',
@@ -91,7 +92,7 @@ for (const [desc, escape] of Object.entries(patterns)) {
 
         const pattern = `${escape}${quantifier}`;
         const range = rewritePattern(pattern, flags, {
-            useUnicodeFlag: flags.includes('u')
+            unicodeFlag: flags.includes('u') ? 'transform' : false,
         });
 
         console.log(`${pattern} => ${range}, flags: ${flags}`);
diff --git a/tools/regexp-generator/package.json b/tools/regexp-generator/package.json
index ba0bf2b161..cffae050be 100644
--- a/tools/regexp-generator/package.json
+++ b/tools/regexp-generator/package.json
@@ -2,23 +2,21 @@
   "name": "test262-regexp-class-escapes",
   "version": "1.0.0",
   "description": "",
-  "main": "index.js",
+  "main": "index.mjs",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1",
     "clean": "rimraf ../../test/built-ins/RegExp/CharacterClassEscapes",
     "prebuild": "mkdirp ../../test/built-ins/RegExp/CharacterClassEscapes",
-    "build": "node index.js"
+    "build": "node index.mjs"
   },
   "author": "",
   "license": "MIT",
-  "dependencies": {
-    "filenamify": "^2.1.0",
-    "jsesc": "^2.5.1",
-    "regexpu-core": "^4.2.0",
-    "slugify": "^1.3.0"
-  },
   "devDependencies": {
+    "filenamify": "^6.0.0",
+    "jsesc": "^3.0.2",
     "mkdirp": "^3.0.1",
-    "rimraf": "^6.0.1"
+    "regexpu-core": "^6.1.1",
+    "rimraf": "^6.0.1",
+    "slugify": "^1.6.6"
   }
 }