diff --git a/packages/markdownlint-config/package.json b/packages/markdownlint-config/package.json
index bd3b064..6d0d509 100644
--- a/packages/markdownlint-config/package.json
+++ b/packages/markdownlint-config/package.json
@@ -1,6 +1,7 @@
 {
   "name": "@ivuorinen/markdownlint-config",
   "version": "0.2.9",
+  "type": "module",
   "description": "ivuorinen's shareable configuration for markdownlint.",
   "author": {
     "name": "Ismo Vuorinen",
@@ -33,7 +34,7 @@
     "url": "https://github.com/ivuorinen/base-configs.git"
   },
   "scripts": {
-    "postinstall": "node scripts/postinstall.js"
+    "postinstall": "node scripts/postinstall.cjs"
   },
   "dependencies": {
     "@ivuorinen/config-checker": "^1.1.4",
diff --git a/packages/markdownlint-config/scripts/postinstall.js b/packages/markdownlint-config/scripts/postinstall.cjs
similarity index 95%
rename from packages/markdownlint-config/scripts/postinstall.js
rename to packages/markdownlint-config/scripts/postinstall.cjs
index aded3b8..f02b022 100644
--- a/packages/markdownlint-config/scripts/postinstall.js
+++ b/packages/markdownlint-config/scripts/postinstall.cjs
@@ -2,6 +2,7 @@
 
 const fs = require('fs')
 const path = require('path')
+// noinspection NpmUsedModulesInstalled
 const process = require('process')
 const checkConfig = require('@ivuorinen/config-checker')
 const foundConfig = checkConfig('markdownlint')