Turbopack Compatibility Error — Fix (2026)

Q: Prevention

Add this to your CLAUDE.md: # Next.js Bundler - Using Turbopack for dev, webpack for production builds. - Do not add webpack plugins to next.config.js without checking Turbopack support. - Use Next.js built-in features (env, redirects, rewrites) instead of webpack plugins.

Last updated: April 20, 2026

The Error

Error: Module not found: Turbopack does not support webpack plugin 'DefinePlugin' in next.config.js
  Unsupported webpack configuration detected. Turbopack only supports a subset of webpack options.

This error occurs when using Next.js with --turbopack flag and your config uses webpack-specific plugins that Turbopack does not support.

The Fix

Remove unsupported webpack plugins from next.config.js:

// next.config.js
/** @type {import('next').NextConfig} */
const nextConfig = {
  // Remove this:
  // webpack: (config) => {
  //   config.plugins.push(new webpack.DefinePlugin({...}));
  //   return config;
  // },
  // Use Next.js env instead:
  env: {
    CUSTOM_VAR: process.env.CUSTOM_VAR,
  },
};
module.exports = nextConfig;

Alternatively, fall back to webpack:

# Remove --turbopack from your dev command
npx next dev
# Instead of: npx next dev --turbopack

Test the build:

npx next build

Why This Happens

Turbopack is Next.js’s Rust-based bundler replacement for webpack. It is faster but does not support the full webpack plugin ecosystem. When Claude generates next.config.js with webpack-specific configurations (DefinePlugin, custom loaders, module federation), Turbopack cannot process them. The feature gap is closing but many webpack plugins remain unsupported.

If That Doesn’t Work

Check which webpack features you use:

grep -A 5 "webpack" next.config.js

Use conditional config for Turbopack vs webpack:

const nextConfig = {
  experimental: {
    turbo: {
      rules: {
        '*.svg': { loaders: ['@svgr/webpack'], as: '*.js' }
      }
    }
  }
};

Check the Turbopack compatibility list for your specific plugins.

Prevention

Add this to your CLAUDE.md:

# Next.js Bundler
- Using Turbopack for dev, webpack for production builds.
- Do not add webpack plugins to next.config.js without checking Turbopack support.
- Use Next.js built-in features (env, redirects, rewrites) instead of webpack plugins.

This fix also applies if you see these related error messages:

Error reading configuration file
JSON parse error in config
Config key not recognized
Module not found: Error: Can't resolve
webpack compiled with 1 error

Frequently Asked Questions

Where does Claude Code store its configuration?

Configuration is stored in ~/.claude/config.json for global settings and .claude/config.json in the project root for project-specific settings. Project settings override global settings for any overlapping keys.

How do I reset Claude Code configuration?

Delete the configuration file and restart Claude Code: rm ~/.claude/config.json && claude. Claude Code recreates the file with default values on next startup. Back up the file first if you have custom settings you want to preserve.

Yes. The project-level .claude/config.json and CLAUDE.md files can be committed to version control. Team members get consistent Claude Code behavior when they check out the repository. Keep API keys and personal preferences in the global config only.

Why does Claude Code’s generated code break webpack builds?

Claude Code may generate import statements that do not match your webpack alias configuration or use Node.js built-in modules that webpack cannot bundle. Add your webpack aliases and resolve configuration to CLAUDE.md so Claude Code generates compatible imports.

Try it: Paste your error into our Error Diagnostic for an instant fix.

Implementation Details

When working with this in Claude Code, pay attention to these practical details:

Project configuration. Add specific instructions to your CLAUDE.md file describing how your project handles this area. Include file paths, naming conventions, and any patterns that differ from common defaults. Claude Code reads CLAUDE.md at the start of every session and uses it to guide all operations.

Testing the setup. After configuration, verify everything works by running a simple test task. Ask Claude Code to perform a read-only operation first (like listing files or reading a config) before moving to write operations. This confirms that permissions, paths, and tools are all correctly configured.

Monitoring and iteration. Track your results over several sessions. If Claude Code consistently makes the same mistake, the fix is usually a more specific CLAUDE.md instruction. If it makes different mistakes each time, the issue is likely in the project setup or toolchain configuration.

Troubleshooting Checklist

When something does not work as expected, check these items in order:

CLAUDE.md exists at the project root — run ls -la CLAUDE.md to verify
Node.js version is 18+ — run node --version to check
API key is set — run echo $ANTHROPIC_API_KEY | head -c 10 to verify (shows first 10 characters only)
Disk space is available — run df -h . to check
Network can reach the API — run curl -s -o /dev/null -w "%{http_code}" https://api.anthropic.com (should return 401 without auth, meaning the server is reachable)
No conflicting processes — run ps aux | grep claude | grep -v grep to check for stale sessions