diff --git a/package.json b/package.json
index 990a4d0..43dd6cb 100644
--- a/package.json
+++ b/package.json
@@ -6,7 +6,7 @@
     "ng": "ng",
     "start": "ng serve",
     "build": "ng build --configuration production",
-    "prebuild": "node src/postbuild.js",
+    "prebuild": "node src/postbuild.mjs",
     "heroku-postbuild": "npm install --prefix backend",
     "test": "ng test",
     "lint": "ng lint",
diff --git a/src/postbuild.js b/src/postbuild.mjs
similarity index 100%
rename from src/postbuild.js
rename to src/postbuild.mjs