The Fix
pip install celery==5.1.1
Based on closed celery/celery issue #6790 · PR/commit linked
Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.
@@ -214,19 +214,24 @@ def handleError(self, record):
def write(self, data):
+ # type: (AnyStr) -> int
"""Write message to logging object."""
if _in_sighandler:
this bug.
Follow the reproduction steps, confirm the failure, apply the fix, and repeat the same steps to verify the behavior changes.
Option A — Upgrade to fixed release\npip install celery==5.1.1\nWhen NOT to use: This fix should not be applied if the application depends on the previous behavior of LoggingProxy.\n\n
Why This Fix Works in Production
- Trigger: Celery breaks libs using `sys.stdout.write()`
- Mechanism: Updates the return type of `LoggingProxy.write()` to conform to `IO.write()` and removes the mutation of written data such as stripping whitespace.
- Why the fix works: Updates the return type of `LoggingProxy.write()` to conform to `IO.write()` and removes the mutation of written data such as stripping whitespace. (first fixed release: 5.1.1).
- If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.
Why This Breaks in Prod
- Production symptom (often without a traceback): Celery breaks libs using `sys.stdout.write()`
Proof / Evidence
- GitHub issue: #6790
- Fix PR: https://github.com/celery/celery/pull/6791
- First fixed release: 5.1.1
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.75
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Hey @ruaridhw :wave:, Thank you for opening an issue”
“An additional, related bug(?) is that Celery mutates the data that is written by calling .strip()”
Failure Signature (Search String)
- Celery breaks libs using `sys.stdout.write()`
- - [x] I have included all related issues and possible duplicate issues
Copy-friendly signature
Failure Signature
-----------------
Celery breaks libs using `sys.stdout.write()`
- [x] I have included all related issues and possible duplicate issues
Error Message
Signature-only (no traceback captured)
Error Message
-------------
Celery breaks libs using `sys.stdout.write()`
- [x] I have included all related issues and possible duplicate issues
Minimal Reproduction
- this bug.
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install celery==5.1.1
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Fix reference: https://github.com/celery/celery/pull/6791
First fixed release: 5.1.1
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix should not be applied if the application depends on the previous behavior of LoggingProxy.
Verify Fix
Follow the reproduction steps, confirm the failure, apply the fix, and repeat the same steps to verify the behavior changes.
Did This Fix Work in Your Case?
Quick signal helps us prioritize which fixes to verify and improve.
Prevention
- Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
- Pin production dependencies and upgrade only with a reproducible test that hits the failing path.
Version Compatibility Table
| Version | Status |
|---|---|
| 5.1.1 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.