Coding⏱️ 3 min read📅 2026-06-04

How to Fix: ng build --prod => Error: Unknown argument: prod

Angular build error due to missing flag

Quick Answer: Use the correct flag for production build, which is '--aot' or '--aotjs' instead of '--prod'.

📋 Table of Contents

  1. 🛑 Root Causes of the Error
  2. ✅ Best Solutions to Fix It
  3. ✨ Wrapping Up

When building an Angular project in production environment, you may encounter an error that prevents your application from compiling. The error 'Unknown argument: prod' is displayed when running the command ng build --prod. This issue affects developers who are using Angular CLI version 10 or higher.

This error can be frustrating as it prevents the compilation of your project, and you cannot serve your application until the issue is resolved.

🛑 Root Causes of the Error

  • The primary reason for this error is that the '--prod' argument has been deprecated in Angular CLI version 10. The new default behavior for the '--prod' flag is to enable production mode automatically when using '--aot'. Therefore, you do not need to specify '--prod' when running ng build.
  • Another possible cause of this error could be an incorrect or missing configuration file (angular.json). If your angular.json file contains a typo or is missing the 'build' section, it can lead to this error.

✅ Best Solutions to Fix It

Using the correct Angular CLI version

  1. Step 1: Update your Angular CLI version to a lower version (version 9 or lower) that still supports the '--prod' argument.
  2. Step 2: Run ng update @angular/cli --force to update your project's dependencies and configurations.
  3. Step 3: Verify that your angular.json file contains the correct configuration for production mode.

Correcting angular.json configuration

  1. Step 1: Open your angular.json file in a text editor and verify that it contains the 'build' section with the correct configuration.
  2. Step 2: Check if the 'aot' option is enabled, as this is the default behavior for production mode in Angular CLI version 10. If not, enable it by adding the '--aot' flag when running ng build.
  3. Step 3: If you still encounter issues, try resetting your project's configurations to their default values using ng config --reset.

✨ Wrapping Up

To resolve the 'Unknown argument: prod' error when building an Angular project in production environment, update your Angular CLI version or correct any configuration errors in your angular.json file. By following these steps, you should be able to successfully compile and serve your application.

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