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

Found 1 possible duplicate issue:

1. https://github.com/anthropics/claude-code/issues/16691

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🤖 Generated with Claude Code

Not the same issue at all.

I'm having the same issue!! HELP!

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"

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

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

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

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

I started getting this error too, WIndows 11 powershell, I can't use Claude Code at all

panic(thread 1441708): integer does not fit in destination type
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

New Claude Code released but still having this issue. Have been unable to use both CLI or VS Code Extension this for days. Please fix this soon 🙏 I have 64gb of system ram and working on a local D drive and still having this issue.

I get the "integer does not fit in destination type" bun 1.3.5 variant as well. No workaround has fixed it. I am on Claude 2.1.14 on Windows, using Terminal, Powershell, and similar variations. All fail. The web interface is unavailable to me as an alternative due to our enterprise IT policy, sadly.

Seeing this issue as well. Not sure if it's related to the Claude Code process exited with code 3 error in the VSCode extension which also started happening recently (link)

For now my workaround is to use wsl instead of powershell or the GUI

Same issue. As summarized by Opus:

Updated Bug Report: Claude Code 2.1.15 crashes on startup with Bun panic on Windows

Summary

Claude Code CLI crashes immediately on startup with a Bun runtime panic (integer does not fit in destination type). Simple flags like --version and --help work, but launching the interactive CLI or any command that loads the full runtime fails.

Environment

|Component |Value |
|-----------------------|---------------------------------------------|
|OS |Windows 11 (Build 10.0.26100.7623) |
|Claude Code Version|2.1.15 |
|Installation Method|Native standalone (installMethod: "native")|
|Binary Location |%USERPROFILE%\.local\bin\claude.exe |
|Binary Size |228,773,024 bytes (~218 MB) |
|Bundled Bun Version|1.3.6 (d530ed99) |
|System RAM |68.60 GB |

CPU Features

CPU: sse42 avx avx2 avx512

Tested Behavior

|Command |Shell |Result |
|-------------------------------|----------|--------------------------------|
|claude --version |PowerShell|✅ Returns 2.1.15 (Claude Code)|
|claude --help |PowerShell|✅ Full help output displayed |
|claude |PowerShell|❌ Bun panic crash |
|claude |CMD |❌ Bun panic crash |
|claude (clean env) |CMD |❌ Bun panic crash |
|claude (from %USERPROFILE%)|PowerShell|❌ Bun panic crash |

Environment Variables Checked

Only unrelated variable present:

CODEX_MANAGED_BY_NPM = 1

No BUN_*, NODE_*, or NPM_* variables set.

Error Output

============================================================
Bun v1.3.6 (d530ed99) Windows x64 (baseline)
Windows v.win11_dt
CPU: sse42 avx avx2 avx512
Args: "claude"
Features: Bun.stderr(2) Bun.stdin(2) Bun.stdout(2) fetch(20) jsc spawn(10) standalone_executable 
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: 1340ms | User: 875ms | Sys: 1375ms
RSS: 2.93GB | Peak: 2.93GB | Commit: 3.05GB | Faults: 720259 | Machine: 68.60GB

panic(thread 36048): integer does not fit in destination type
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

Bun Crash Report URL

https://bun.report/1.3.6/e_1d530ed9GugogCsulmM6/1qJg6pqMCYKERNEL32.DLLut0LCSntdll.dll4zijBA0eNoFwcENACAMAsBVWM1ENHyosXzc3js53LyYxYYrWApkTHbkEZWRd/gBNAAPKQ

Memory State at Crash (Consistent Across Tests)

|Metric |Range |
|-----------|---------------|
|RSS |2.88–2.93 GB |
|Peak |2.88–2.93 GB |
|Commit |2.96–3.05 GB |
|Page Faults|709,733–720,259|

Key Observations

1. Consistent crash: Every invocation that loads the full runtime crashes identically
2. Same crash signature: Thread ID varies, but panic message and memory profile are consistent
3. Pre-runtime crash: Occurs before any user code, project, or config is loaded
4. Shell-independent: Crashes in both PowerShell and CMD
5. Environment-independent: Clean environment makes no difference
6. Directory-independent: Working directory doesn’t affect crash

Probable Cause

The panic integer does not fit in destination type combined with:

• High memory consumption (~2.9 GB) before crash
• Involvement of KERNEL32.DLL and ntdll.dll
• AVX-512 capable CPU

…suggests an integer overflow in Bun 1.3.6’s memory allocation or SIMD code paths, possibly triggered by:

• Windows 11 24H2 (Build 26100) memory management changes
• AVX-512 specific code paths
• Large standalone executable unpacking

Related Issues

• Bun issue tracker should be checked for similar Bun 1.3.6 panics on Windows
• This may be related to known Bun 1.3.x Windows regressions

Requested Actions

1. Immediate: Provide a way to downgrade to a previous Claude Code version with working Bun runtime
2. Short-term: Consider bundling Bun 1.2.x until 1.3.x Windows issues are resolved
3. Investigation: Test Claude Code 2.1.15 on Windows 11 24H2 with AVX-512 CPUs

Workaround Requests

• Is there an npm-based installation method that uses system Node.js instead of bundled Bun?
• Can a previous version of Claude Code be manually installed?
• Are there environment variables to force Bun to use different code paths (e.g., disable AVX-512)?

Downgrade attempt summary

• Tried installing Claude Code v2.0.76 to avoid Bun 1.3.x using:

``powershell
& ([scriptblock]::Create((irm https://claude.ai/install.ps1))) 2.0.76
``

• Installer reported success, then crashed with a Bun panic:

``text
panic(thread ...): integer does not fit in destination type
``

• Crash output indicates Bun v1.3.6 is running the installer binary with:

``text
Args: "C:\Users\ryant\.claude\downloads\claude-2.1.15-win32-x64.exe" "install" "2.0.76"
``

• Result: The downgrade path still uses the Bun 1.3.6 installer (claude-2.1.15 .exe) and crashes the same way, so it doesn’t avoid the Bun 1.3.x crash.

Also having the same problem, seems to be after a few windows updates that were rolled out on my machine yesterday afternoon

Workaround: temporarily switch back to the npm installation of Claude Code

We're planning to update the included version of bun to include this fix ASAP, but need to address a few blockers first.

Title: Bun panic on Windows: "integer does not fit in destination type" in
preadv

Body:
## Environment

• Bun version: 1.3.5
• OS: Windows x86_64
• Context: Running Claude Code (npm) which uses Bun internally

## Error
panic: integer does not fit in destination type

• sys_uv.zig:294: preadv
• node_fs.zig:5168: readFileWithOptions
• atomic.zig:50: fetchSub

Features: spawn, standalone_executable, process_dlopen, Bun.stderr, Bun.stdin,
Bun.stdout, fetch, jsc

## Steps to Reproduce

1. Install Claude Code via npm: npm install -g @anthropic-ai/claude-code
2. Run claude in a project directory on Windows
3. Crash occurs during file reading operations

## Expected Behavior
File reading should complete without panic.

## Notes
This appears to be an integer overflow in the preadv syscall wrapper on
Windows.

Well, present, one more on the list of those affected.

Same here. Waiting for a fix!

UPDATE (at least from my side):
Fix confirmed for Windows 11 25H2

The crash is caused by Windows Update KB5074109 (Jan 14, 2026) breaking Bun v1.3.5.

My specs:

• Windows 11 25H2
• Claude Code Desktop App v2.1.15/v2.1.17
• KB5074109 installed Jan 14, 2026

Solution: Install Microsoft's out-of-band update KB5077744

1. Download from Microsoft Update Catalog
2. Install via PowerShell (Admin):

``powershell
wusa.exe "path\to\windows11.0-kb5077744-x64_fb63f62e4846b81b064c3515d7aff46c9d6d50c8.msu" /quiet
``

1. Restart

| Windows Version | Fix |
|-----------------|-----|
| 25H2 / 24H2 | KB5077744 |
| 23H2 | KB5077797 |

Has anyone tried switching to the npm installation instead of the Native Installer? Claude suggests I try it, but that my expectations shouldn't be too high since it has the same dependency on bun.

Has anyone tried switching to the npm installation instead of the Native Installer? Claude suggests I try it, but that my expectations shouldn't be too high since it has the same dependency on bun.

Yes, npm works.

Has anyone tried switching to the npm installation instead of the Native Installer? Claude suggests I try it, but that my expectations shouldn't be too high since it has the same dependency on bun.

I can confirm the issue went away for me after switching to the npm install. Used claude web to give me step by step on how to uninstall native and backup settings

+1 experiencing this issue

Environment:

• Windows 11
• Claude Code v2.1.17 (CLI and VS Code extension)
• Machine RAM: 51.25GB
• Bundled Bun: v1.3.5

Crash details:

• Both CLI and VS Code extension crash
• Happens during "thinking" phase with Opus 4.5
• RSS reaches ~4.42GB before crash

Crash log:
Bun v1.3.5 (1e86cebd) Windows x64 (baseline)
panic(thread): integer does not fit in destination type
https://bun.report/1.3.5/e_11e86cebmgEugogCw+kiM65ioJgqpmMCYKERNEL32.DLLut0LCSntdll.dll4zijBA0eNoFwcENACAMAsBVWM1ENHyosXzc3js53LyYxYYrWApkTHbkEZWRd/gBNAAPKQ

Requesting priority update to Bun 1.3.6 which has the fix.

@ant-kurt Feel free to close the comments section for now if you think there is no further information to add. This will prevent more people from saying they are experiencing the same problem. Now that your teams are aware of the issue, the spam is no longer useful. Plus, it seems that your workaround with the npm installation is working.

edit: Keep the issue open, though, so that we can keep track of it.

Investigation Results

I investigated the bundled Bun version across different Claude Code releases:

| Version | Location | Embedded Bun |
|:-------:|:---------|------------:|
| 2.1.7 | .vscode/extensions/ | 1.3.5 |
| 2.1.21 | .vscode/extensions/ | 1.3.5 |

All versions (including the latest 2.1.21) still bundle Bun v1.3.5.

Interesting Finding

Both 2.1.7 and 2.1.21 use Bun 1.3.5, but:

• 2.1.7: No crash observed
• 2.1.21: Crash occurs

The bundled JavaScript code is different (different file sizes and hashes), suggesting that new code in 2.1.21 may trigger the Bun bug more frequently due to different file I/O patterns, memory usage, or code paths.

Crash Report

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

Relevant Bun Fixes

Bun v1.3.6 (Release Notes)

Fixed: "integer does not fit in destination type" error when reading files that are modified by another process or on network drives, where libuv returns unmapped error codes like UV_UNKNOWN

Speculative fix: crash on Windows machines at start when very little memory is available

Bun v1.3.7 (Release Notes)

• Fixed integer overflow when reading/writing files larger than 4GB
• Fixed bytecode cache alignment issues on Windows PE sections

Request

Would it be possible to rebuild the native binary with Bun v1.3.6 or later? The fix has been available since January 13, 2026.

Environment

• OS: Windows 11
• IDE: VSCode 1.96.4
• Claude Code Extension: 2.1.21
• Embedded Bun: 1.3.5
• Latest Bun: 1.3.7

<img width="563" height="867" alt="Image" src="https://github.com/user-attachments/assets/2d02e7f1-6367-4e92-a6e2-b7a6a61c6ccc" />

Updating to KB5077744 (Out of Band Update) fixed this for me. Thanks @D-Ac3

Edit: This appears to have re-broken short after this update, due to another update. I guess npm (rather than native) is the way to go for now.

tried it on the first day of the bun release, and again today. still same problem.
used NPM until now without a problem since my first attempt, i have to go back to NPM again

Indeed this has been happening for a while now and keeps happening with Windows native build. Using the npm version and it works well. Please don't deprecate the npm version because we'd be unable to use claude coda.

Here's my (currently working) workaround to get it working on NPM on v2.1.29 (latest)
NOTE - the below is generated by claude.ai (web interface) after a compact. it may (and probably does) include incorrect steps. use if you have no other option. it was quite painful.

----------------

Workaround: npm install bypasses the Bun crash

The native installer bundles Bun 1.3.5 which has this crash. The npm package uses Node.js instead, so it avoids the bug entirely.

Steps

1. Remove the native installer binary:

Remove-Item -Force "$env:USERPROFILE\.local\bin\claude.exe" -ErrorAction SilentlyContinue
Remove-Item -Force "$env:USERPROFILE\.local\bin\claude" -ErrorAction SilentlyContinue

2. Clear cached native downloads (important — the npm package will try to bootstrap the native binary otherwise):

Remove-Item -Recurse -Force "$env:USERPROFILE\.claude\downloads" -ErrorAction SilentlyContinue

3. Install via npm (requires Node.js 18+):

npm install -g @anthropic-ai/claude-code@latest

4. Verify:

claude --version

Notes

• Same version (2.1.29), different runtime — Node.js instead of Bun
• You'll see a deprecation banner ("Claude Code has switched from npm to native installer") — ignore it, this is the workaround
• Your existing config (~/.claude.json) and project settings are preserved
• This is a temporary fix until Anthropic ships a build with Bun ≥1.3.6
• Had Api 500 error, fixed by restarting PC

Environment

• Windows

Also affected — Bun 1.3.5 segfault on Windows 11 (native standalone installer)
Every time I run the standalone installer (irm https://claude.ai/install.ps1 | iex), it crashes with the same Bun 1.3.5 segfault:
panic(thread 25500): Segmentation fault at address 0x3C
The npm install (npm install -g @anthropic-ai/claude-code) works and Claude Code runs fine, but Shift+Tab keybindings don't work on the npm version in Windows Terminal — PowerShell passes the keypress correctly (confirmed with [Console]::ReadKey), but Claude Code doesn't receive it. Alt+M works as a workaround.
This seems to be because the npm build handles terminal input differently to the native build. So the Bun crash is blocking both the native install AND proper keyboard shortcut support.
Would really appreciate getting Bun 1.3.6+ bundled so the native installer stops crashing.
Environment:

Windows 11 (Build 26200)
PowerShell 7.5.4
Windows Terminal
Claude Code 2.1.31 (npm-global)
CPU: sse42 avx avx2 avx512

Per email from Anthropic Support Team:

Thanks for reaching out and sincere apologies for the delay here - we’re working hard to restore our typical response times. Please run claude update to get the latest version of Claude Code. The bun panic error "integer does not fit in destination type" is a known issue with Bun v1.3.5 on Windows that has been addressed in subsequent releases.

Mentioned version is probably 2.1.32, released today. But it's hard to know for sure, as I don't see anything in the CHANGELOG that points in that direction.

If anyone from Anthropic or anyone else experiencing this issue can confirm whether or not it has been resolved, that would help move things forward (since I haven't encountered the problem since I used the workaround).

Per email from Anthropic Support Team: > Thanks for reaching out and sincere apologies for the delay here - we’re working hard to restore our typical response times. > Please run claude update to get the latest version of Claude Code. The bun panic error "integer does not fit in destination type" is a known issue with Bun v1.3.5 on Windows that has been addressed in subsequent releases. Mentioned version is probably 2.1.32, released today. But it's hard to know for sure, as I don't see anything in the CHANGELOG that points in that direction. If anyone from Anthropic or anyone else experiencing this issue can confirm whether or not it has been resolved, that would help move things forward (since I haven't encountered the problem since I used the workaround).

have you tried updating? is the bug solved there?

thanks for sharing

Yes it did fix it. It seems the newer version of bun and a fresh install seemed to sort it out. Phew was getting worried there!

yep works for me too now! and has opus4.6 thanks mate.
happy shipping

I can still reproduce the same Bun panic from #18567 on Windows with newer Claude Code.

Environment

• Claude Code: 2.1.34
• OS: Windows 11
• Shell: PowerShell
• Bundled Bun shown at crash: 1.3.5

Crash signature

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

Observed behavior

• Claude starts and can sometimes accept initial input.
• Then Bun crashes with the same panic.
• Crash output shows very high memory usage (multi-GB RSS/Peak).

Additional data point

In my case, very large local Claude session files existed under .claude/projects (multiple files around 0.5GB to >2GB each). Moving those oversized files out of the active projects directory made the crash stop immediately.

Minimal repro direction

1. Windows 11 + Claude Code 2.1.34
2. Have very large session artifacts under .claude/projects (hundreds of MB to multi-GB)
3. Run claude
4. Observe panic: integer does not fit in destination type

This looks like the same underlying Bun panic as #18567, potentially with a broader trigger set related to large local state.

Hello, I can confirm that I managed to upgrade from npm to native installer in Windows 11 (using powershell 7) and everything seems to work fine again

Update: Regression on Bun 1.3.9-canary
Previously confirmed that upgrading to Bun 1.3.8 (via irm https://claude.ai/install.ps1 | iex) completely fixed both the segfault and Shift+Tab keybindings on the native build. Everything was rock solid.
Now on Bun Canary v1.3.9-canary.51 (d5628db2), the segfault is back — same address 0x3C, same USER32.dll stack trace. Key difference: it's not crashing on startup like the old 1.3.5 bug. Claude Code runs fine, Shift+Tab still works, but it segfaulted mid-session after ~20 minutes of use. Restarted and it's fine again.
Crash report: https://bun.report/1.3.9/e_2d5628dbmgkgEuhogCCYnpggNT64.desy2TCYnpggNT64.desynouE__CYnpggNT64.desws0PCUUSER32.dllgg1vBCYnpggNT64.desgi6R____CYnpggNT64.desoqmWA2A4D
Environment:

Windows 11
Bun Canary v1.3.9-canary.51 (d5628db2)
CPU: sse42 avx avx2 avx512
RSS at crash: 0.78GB / Peak: 1.03GB

TL;DR: 1.3.8 stable = solid. 1.3.9-canary = regression. Not a blocker (restarts fine) but something got reintroduced between those versions.

Hit this too on Windows 11. Switching to npm i -g @anthropic-ai/claude-code fixed it — avoids Bun entirely.

Also swapped my statusline plugin for cc-hud (pure Node.js, no deps). Rock solid now.

Environment: Windows 11, Claude Code CLI
Error: Bun crash on startup
Workaround: WSL2 Ubuntu (functional but not ideal)

This is a blocker for Windows users.
Please prioritize a fix.

Any solution for this?
I am also facing the same with my team members.

============================================================
Bun v1.3.14 (0a466a11) Windows x64 (baseline)
Windows v.win11_ge
CPU: sse42 avx avx2
Args: "claude"
Features: Bun.stderr(2) Bun.stdin(2) Bun.stdout(2) fetch(5) jsc spawn(4) standalone_executable yaml_parse claude_code
Builtins: "bun:ffi" "bun:main" "node:assert" "node:async_hooks" "node:buffer" "node:child_process" "node:crypto" "node:dns" "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:readline" "node:stream" "node:stream/consumers" "node:string_decoder" "node:timers/promises" "node:tls" "node:tty" "node:url" "node:util" "node:vm" "node:zlib" "ws" "node:http2"
Elapsed: 2528ms | User: 265ms | Sys: 203ms
RSS: 0.39GB | Peak: 0.39GB | Commit: 0.47GB | Faults: 100705 | Machine: 33.76GB
 
panic(thread 40416): Segmentation fault at address 0xCC
 
panic: Segmentation fault at address 0xC8
panicked during a panic. Aborting.

Any solution for this? I am also facing the same with my team members. `` ============================================================ Bun v1.3.14 (0a466a11) Windows x64 (baseline) Windows v.win11_ge CPU: sse42 avx avx2 Args: "claude" Features: Bun.stderr(2) Bun.stdin(2) Bun.stdout(2) fetch(5) jsc spawn(4) standalone_executable yaml_parse claude_code Builtins: "bun:ffi" "bun:main" "node:assert" "node:async_hooks" "node:buffer" "node:child_process" "node:crypto" "node:dns" "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:readline" "node:stream" "node:stream/consumers" "node:string_decoder" "node:timers/promises" "node:tls" "node:tty" "node:url" "node:util" "node:vm" "node:zlib" "ws" "node:http2" Elapsed: 2528ms | User: 265ms | Sys: 203ms RSS: 0.39GB | Peak: 0.39GB | Commit: 0.47GB | Faults: 100705 | Machine: 33.76GB panic(thread 40416): Segmentation fault at address 0xCC panic: Segmentation fault at address 0xC8 panicked during a panic. Aborting. ``

Install native . If can uninstall claude code cause their support is poor and ban wave for nothing