Next.js "JavaScript heap out of memory" during next build in CI

By Kaveh Alemi·Latchkey

next build runs in Node, and compiling a large application can exceed V8's default heap limit. Node then aborts with a fatal out-of-memory error, killing the build regardless of how much RAM the runner has.

What this error means

next build crashes with "FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory" and exit code 134 or 137, often only on bigger pages or after dependency growth.

<--- Last few GCs --->
[1234:0x...]  FATAL ERROR: Reached heap limit Allocation failed -
JavaScript heap out of memory
 1: 0xb7... node::Abort()

Common causes

The build exceeds V8's default heap size

Node caps the old-space heap; a large bundle, many pages, or heavy source maps can push allocation past the limit and abort.

The runner has too little memory for the build

A small runner (for example 2 vCPU / few GB) is killed by the kernel (exit 137) before the build finishes.

How to fix it

Raise the Node heap limit for the build

1. Set NODE_OPTIONS to increase the old-space size for the build step.
2. Choose a value that fits within the runner's real memory.
3. Re-run next build.

env:
  NODE_OPTIONS: --max-old-space-size=4096

Reduce memory pressure or use a larger runner

Disable production source maps if not needed and run the build on a runner with more RAM.

// next.config.js
module.exports = { productionBrowserSourceMaps: false }

How to prevent it

• Set a sensible --max-old-space-size for large builds in CI.
• Right-size the runner so the heap limit fits in real memory.
• Avoid shipping unneeded production source maps.

Frequently asked questions

Related guides

References

• Node.js documentation
• npm CLI documentation
• GitHub Actions documentation