[BUG] Bun v1.3.5 crashes on Windows with "integer does not fit in destination type" - prevents installation and startup

[Dyl-M]

Preflight Checklist

• I have searched existing issues and this hasn't been reported yet
• This is a single bug report (please file separate reports for different bugs)
• I am using the latest version of Claude Code

What's Wrong?

Claude Code crashes immediately on startup and during installation on Windows 11 with a Bun runtime panic: integer does not fit in destination type. This affects both running Claude Code and attempting fresh installs via the PowerShell installer script.

The crash occurs in the bundled Bun v1.3.5 runtime. This specific bug was fixed in Bun v1.3.6 (released January 13, 2026), which includes a fix for this exact error when reading files on Windows systems with limited memory or on network drives.

What Should Happen?

Claude Code should start normally and installation should complete without Bun crashes.

Error Messages/Logs

Bun v1.3.5 (1e86cebd) Windows x64 (baseline)
Windows v.win11_dt
CPU: sse42 avx avx2
Args: "C:\Users\foo\.local\bin\claude.exe"
Features: Bun.stderr(2) Bun.stdin(2) Bun.stdout(2) fetch(33) jsc spawn(20) standalone_executable process_dlopen
Builtins: "bun:main" "node:assert" "node:async_hooks" "node:buffer" "node:child_process" "node:constants" "node:crypto" "node:domain" "node:events" "node:fs" "node:fs/promises" "node:http" "node:https" "node:module" "node:net" "node:os" "node:path" "node:path/posix" "node:path/win32" "node:perf_hooks" "node:process" "node:querystring" "node:stream" "node:timers/promises" "node:tls" "node:tty" "node:url" "node:util" "node:zlib" "node:worker_threads" "undici" "ws" "node-fetch" "node:inspector" "node:http2" "node:diagnostics_channel"
Elapsed: 5272ms | User: 2390ms | Sys: 3390ms
RSS: 3.21GB | Peak: 3.22GB | Commit: 3.30GB | Faults: 797032 | Machine: 16.60GB

panic(thread 1552): integer does not fit in destination type
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

Steps to Reproduce

1. Run Claude Code on Windows 11: claude or attempt fresh install irm https://claude.ai/install.ps1 | iex
2. Observe crash with Bun

Claude Model

Other

Is this a regression?

Yes, this worked in a previous version

Last Working Version

No response

Claude Code Version

2.1.9

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

• Bundled Bun Version: 1.3.5 (needs to be upgraded from Claude Code itself)
• Machine RAM: 16.60GB

[github-actions]

Found 1 possible duplicate issue:

1. [Bug] Claude in Chrome Native Host crashes on Windows 11 - Bun internal assertion failure #16691

This issue will be automatically closed as a duplicate in 3 days.

• If your issue is a duplicate, please close it and 👍 the existing issue instead
• To prevent auto-closure, add a comment or 👎 this comment

🤖 Generated with Claude Code

[Dyl-M]

Not the same issue at all.

[davistroy]

I'm having the same issue!! HELP!

[davistroy]

I fixed it, but this is the nuclear option - don't blame me if you use this (Powershell 7):

Remove-Item -Recurse -Force "$env:USERPROFILE.claude"

[mattroper]

Same for me - unable to launch/update Claude on Windows.

Bun v1.3.5 (1e86cebd) Windows x64 (baseline)
panic(thread 10984): integer does not fit in destination type

[Dovidc]

Same issue:

panic(thread 16352): integer does not fit in destination type

2026-01-18 13:12:28.237 [info] From claude: oh no: Bun has crashed. This indicates a bug in Bun, not your code.

To send a redacted crash report to Bun's team,
please file a GitHub issue using the link below:

 
2026-01-18 13:12:28.238 [info] From claude: https://bun.report/1.3.5/e_11e86cebGugogCw+kiM65ioJgqpmMCYKERNEL32.DLLut0LCSntdll.dll4zijBA0eNoFwcENACAMAsBVWM1ENHyosXzc3js53LyYxYYrWApkTHbkEZWRd/gBNAAPKQ

[HellCatVN]

panic(thread 6124): integer does not fit in destination type
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

To send a redacted crash report to Bun's team,
please file a GitHub issue using the link below:

https://bun.report/1.3.5/e_11e86cebGugogCw+kiM65ioJgqpmMCYKERNEL32.DLLut0LCSntdll.dll4zijBA0eNoFwcENACAMAsBVWM1ENHyosXzc3js53LyYxYYrWApkTHbkEZWRd/gBNAAPKQ

[davistroy]

happened again to me out of the blue - had to use nuclear option again ... PITA