Fix Claude Code Bun Errors

Written by Michael Lip · Solo founder of Zovo · $400K+ on Upwork · 100% JSS Join 50+ builders · More at zovo.one

Last updated: April 17, 2026

Claude Code can throw various Bun-specific errors during installation, startup, or runtime. This guide covers the most common Bun error messages and provides targeted fixes for each one.

The Problem

You are running Claude Code with Bun and encountering errors like ModuleNotFound, TypeError, ENOENT, or Bun-specific resolution failures. Unlike crashes (which kill the process), these errors produce error messages but may leave Claude Code in a broken state where commands fail silently or produce incorrect results.

Quick Solution

Step 1: Identify the exact error. Run Claude Code with stderr visible:

claude 2>&1 | head -50

Step 2: If the error mentions module resolution (e.g., ModuleNotFound or Cannot find module), reinstall dependencies:

rm -rf node_modules bun.lockb
bun install

Step 3: If the error involves a specific package, check Bun compatibility. Some packages need the --backend=copyfile flag:

bun install --backend=copyfile

Step 4: If you see TypeError: X is not a function, this is usually a Bun polyfill gap. Check if the missing function is a Node.js built-in that Bun has not fully implemented. Verify against the Bun compatibility table.

Step 5: As a quick workaround, force Claude Code to use Node.js for the current session:

NODE_PATH=$(which node) npx claude

How It Works

Bun reimplements the Node.js runtime from scratch using JavaScriptCore and Zig. While it targets full Node.js API compatibility, gaps remain in edge cases — particularly around node: built-in modules, Worker threads, some crypto functions, and advanced fs operations. Claude Code depends on a tree of npm packages, each of which may exercise different parts of the Node.js API. When one of those packages calls a function Bun has not implemented or implements differently, you get a runtime error. These errors are typically deterministic: the same operation will fail every time until the Bun version adds support or you switch to Node.js.

Common Issues

bun.lockb conflicts with package-lock.json. If your project has both lockfiles, Bun may resolve different dependency versions than expected. Remove one lockfile and stick with a single package manager:

rm package-lock.json
bun install

ENOENT on postinstall scripts. Some packages run shell scripts during install that assume bash paths. On systems where /bin/sh is not bash, these can fail under Bun. Fix by ensuring bash is available:

which bash

If missing (rare on macOS, possible in containers), install bash or skip postinstall:

bun install --ignore-scripts

crypto.subtle or webcrypto errors. If Claude Code or its dependencies use crypto.subtle and Bun throws an error, this is a known gap in older Bun versions. Update Bun:

bun upgrade

Example CLAUDE.md Section

# Bun Runtime Error Handling

## Package Manager
- Using Bun for package management and runtime
- Lockfile: bun.lockb (do not mix with package-lock.json)
- Install command: bun install

## Known Bun Gaps for This Project
- node:worker_threads — limited support, avoid in hot paths
- node:vm — not fully implemented, some eval patterns may fail
- Native addons (.node files) — require Bun napi support

## Error Debugging
- Run with stderr: claude 2>&1 | head -50
- Check Bun compat: https://bun.sh/docs/runtime/nodejs-apis
- Fallback to Node.js if blocked: npx claude

## Dependencies
- All deps verified working with Bun 1.1+
- If adding new deps, test with: bun run test

Best Practices

Lock your Bun version in CI. Use a .bun-version file or pin the version in your Dockerfile to avoid surprises when Bun auto-updates.
Test after Bun upgrades. When you run bun upgrade, immediately test Claude Code with a simple prompt. New Bun versions occasionally introduce regressions.
Keep a Node.js fallback ready. Have Node.js installed alongside Bun. When a Bun error blocks your work, switching runtimes takes seconds and gets you unblocked immediately.
Check Bun’s GitHub issues before filing. Most Bun compatibility errors are already tracked. Search github.com/oven-sh/bun/issues with the error message to find existing fixes or workarounds.
Prefer Node.js APIs over Bun-specific APIs in shared code. If you write scripts or hooks that Claude Code runs, stick to standard Node.js APIs for maximum compatibility.

I'm a solo developer in Vietnam. 50K Chrome extension users. $500K+ on Upwork. 5 Claude Max subscriptions running agent fleets in parallel. These are my actual CLAUDE.md templates, orchestration configs, and prompts. Not a course. Not theory. The files I copy into every project before I write a line of code. **[See what's inside →](https://zovo.one/lifetime?utm_source=ccg&utm_medium=cta-default&utm_campaign=claude-code-bun-error)** $99 once. Free forever. 47/500 founding spots left.