diff --git a/package.json b/package.json
index fe4762719..f1f5ef087 100644
--- a/package.json
+++ b/package.json
@@ -2,6 +2,7 @@
   "private": true,
   "name": "monorepo-deploy-actions",
   "license": "MIT",
+  "type": "module",
   "devDependencies": {
     "@eslint/js": "9.15.0",
     "@tsconfig/recommended": "1.0.8",
diff --git a/update-outdated-pull-request-branch/jest.config.js b/update-outdated-pull-request-branch/jest.config.js
index 4f97e5f78..f6a60fb23 100644
--- a/update-outdated-pull-request-branch/jest.config.js
+++ b/update-outdated-pull-request-branch/jest.config.js
@@ -1,7 +1,9 @@
-module.exports = {
-  preset: 'ts-jest',
+/** @type {import('ts-jest').JestConfigWithTsJest} */
+export default {
+  preset: 'ts-jest/presets/default-esm',
   clearMocks: true,
-  testEnvironment: 'node',
-  testMatch: ['**/*.test.ts'],
-  verbose: true,
+  // https://kulshekhar.github.io/ts-jest/docs/guides/esm-support/
+  moduleNameMapper: {
+    '^(\\.{1,2}/.*)\\.js$': '$1',
+  },
 }
diff --git a/update-outdated-pull-request-branch/package.json b/update-outdated-pull-request-branch/package.json
index dc7ba5a10..739f1e8df 100644
--- a/update-outdated-pull-request-branch/package.json
+++ b/update-outdated-pull-request-branch/package.json
@@ -2,6 +2,7 @@
   "name": "update-outdated-pull-request-branch",
   "version": "0.0.0",
   "private": true,
+  "type": "module",
   "scripts": {
     "build": "ncc build --source-map --license licenses.txt src/main.ts",
     "test": "jest"
diff --git a/update-outdated-pull-request-branch/src/main.ts b/update-outdated-pull-request-branch/src/main.ts
index 97bf052a1..66182852e 100644
--- a/update-outdated-pull-request-branch/src/main.ts
+++ b/update-outdated-pull-request-branch/src/main.ts
@@ -1,6 +1,6 @@
 import * as core from '@actions/core'
 import * as github from '@actions/github'
-import { run } from './run'
+import { run } from './run.js'
 import assert from 'assert'
 
 const main = async (): Promise<void> => {
diff --git a/update-outdated-pull-request-branch/tests/run.test.ts b/update-outdated-pull-request-branch/tests/run.test.ts
index bf952f752..362366bb0 100644
--- a/update-outdated-pull-request-branch/tests/run.test.ts
+++ b/update-outdated-pull-request-branch/tests/run.test.ts
@@ -1,4 +1,4 @@
-import { isExpired } from '../src/run'
+import { isExpired } from '../src/run.js'
 
 describe('isExpired', () => {
   const now = () => Date.parse('2021-02-03T04:05:06Z')