`experimental.cssChunking: "strict"` is only supported with

Error message

`experimental.cssChunking: "strict"` is only supported with webpack. Please remove the option or run Next.js with webpack in ${configFileName}.

What it means

`experimental.cssChunking: "strict"` is a webpack-only strategy. If the resolved mode is 'strict' and Turbopack is active, normalization throws. Skipped during `next start` and PHASE_INFO. This is the mirror of the graph-mode Turbopack-only constraint.

Source

Thrown at packages/next/src/server/config.ts:527

        `Please remove the "functions" property from your sassOptions in ${configFileName}.`
    )
  }

  // Validate experimental.cssChunking compatibility with the active bundler. Graph mode is
  // Turbopack-only; strict mode and `false` (single-chunk-per-module) are webpack-only.
  // Only validate during build/dev — `next start` doesn't pick a bundler and would otherwise
  // see `process.env.TURBOPACK` unset and reject a valid `cssChunking: "graph"` config.
  if (phase !== PHASE_PRODUCTION_SERVER && phase !== PHASE_INFO) {
    const cssChunkingValue = result.experimental.cssChunking
    const cssChunkingMode = resolveCssChunkingMode(cssChunkingValue)
    if (cssChunkingMode === 'graph' && !process.env.TURBOPACK) {
      throw new Error(
        `\`experimental.cssChunking: "graph"\` is only supported with Turbopack. ` +
          `Please remove the option or run Next.js with Turbopack in ${configFileName}.`
      )
    }
    if (cssChunkingMode === 'strict' && process.env.TURBOPACK) {
      throw new Error(
        `\`experimental.cssChunking: "strict"\` is only supported with webpack. ` +
          `Please remove the option or run Next.js with webpack in ${configFileName}.`
      )
    }
    // Only error when `false` was set explicitly. `undefined` (the default) also resolves to
    // `'off'` but that's the implicit default and must not error on Turbopack.
    if (cssChunkingValue === false && process.env.TURBOPACK) {
      throw new Error(
        `\`experimental.cssChunking: false\` is only supported with webpack. ` +
          `Please remove the option or run Next.js with webpack in ${configFileName}.`
      )
    }

    if (
      result.experimental.turbopackRustReactCompiler &&
      !process.env.TURBOPACK
    ) {
      throw new Error(

View on GitHub (pinned to 0ae8c72462)

Solutions

Run with webpack: `next build --webpack`
Remove the cssChunking option (let it default) or set it to a Turbopack-supported value like 'graph'

Example fix

// before
// next build  (Turbopack)
module.exports = { experimental: { cssChunking: 'strict' } }
// after (option A)
module.exports = { experimental: { cssChunking: 'graph' } }
// after (option B)
module.exports = {}
// run: next build --webpack

Defensive patterns

Strategy: validation

Validate before calling

const isTurbopack = Boolean(process.env.TURBOPACK)
if (cssChunking === 'strict' && isTurbopack) {
  cssChunking = undefined // or switch to webpack
}

Prevention

Conditionally set cssChunking based on the bundler
Avoid sharing one cssChunking value across webpack and Turbopack projects

When it happens

Trigger: Setting `experimental: { cssChunking: 'strict' }` and running `next dev`/`next build` with Turbopack (the default bundler).

Common situations: Copying a webpack-era cssChunking config into a project now on Turbopack. Sharing a config file between webpack and Turbopack branches.

Related errors

AI-assisted analysis of vercel/next.js@0ae8c72462 (2026-08-06). Data as JSON: /api/errors/08850e068eb45660. Report an issue: GitHub.