The Fix
pip install celery==5.2.0rc2
Based on closed celery/celery issue #6910 · 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.
@@ -206,6 +206,7 @@ def detach(path, argv, logfile=None, pidfile=None, uid=None,
'--events',
is_flag=True,
+ default=None,
cls=CeleryOption,
help_group="Pool Options",
repro.py
software -> celery:5.2.0b1 (sun-harmonics) kombu:5.1.0 py:3.7.5
billiard:3.6.4.0 py-amqp:5.0.6
platform -> system:Linux arch:64bit, ELF
kernel version:5.4.0-77-generic imp:CPython
loader -> celery.loaders.app.AppLoader
settings -> transport:pyamqp results:disabled
broker_url: 'amqp://guest:********@localhost:5672//'
deprecated_settings: None
worker_send_task_events: True
verify
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
fix.md
Option A — Upgrade to fixed release\npip install celery==5.2.0rc2\nWhen NOT to use: Do not apply this fix if the CLI argument is intentionally set to False.\n\n
Why This Fix Works in Production
- Trigger: - [x] I have included all related issues and possible duplicate issues
- Mechanism: Changes the default value of the --task-events flag from implicit False to explicit None, allowing the correct resolution of task events based on app.conf settings.
- Why the fix works: Changes the default value of the --task-events flag from implicit False to explicit None, allowing the correct resolution of task events based on app.conf settings. (first fixed release: 5.2.0rc2).
Production impact:
- 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): - [x] I have included all related issues and possible duplicate issues
Proof / Evidence
- GitHub issue: #6910
- Fix PR: https://github.com/celery/celery/pull/6966
- First fixed release: 5.2.0rc2
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.59
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Hey @AlexHill :wave:, Thank you for opening an issue”
Failure Signature (Search String)
- - [x] I have included all related issues and possible duplicate issues
- or possible duplicates to this issue as requested by the checklist above.
Copy-friendly signature
signature.txt
Failure Signature
-----------------
- [x] I have included all related issues and possible duplicate issues
or possible duplicates to this issue as requested by the checklist above.
Error Message
Signature-only (no traceback captured)
error.txt
Error Message
-------------
- [x] I have included all related issues and possible duplicate issues
or possible duplicates to this issue as requested by the checklist above.
Minimal Reproduction
repro.py
software -> celery:5.2.0b1 (sun-harmonics) kombu:5.1.0 py:3.7.5
billiard:3.6.4.0 py-amqp:5.0.6
platform -> system:Linux arch:64bit, ELF
kernel version:5.4.0-77-generic imp:CPython
loader -> celery.loaders.app.AppLoader
settings -> transport:pyamqp results:disabled
broker_url: 'amqp://guest:********@localhost:5672//'
deprecated_settings: None
worker_send_task_events: True
What Broke
Task events cannot be enabled via app configuration, leading to missing event data.
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install celery==5.2.0rc2
When NOT to use: Do not apply this fix if the CLI argument is intentionally set to False.
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Option D — Guard side-effects with OnceOnly Guardrail for side-effects
Mitigate duplicate external side-effects under retries/timeouts/agent loops by gating the operation before calling external systems.
- Place OnceOnly between your code/agent and real side-effects (Stripe, emails, CRM, APIs).
- Use a stable key per side-effect (e.g., customer_id + action + idempotency_key).
- Fail-safe: configure fail-open vs fail-closed based on blast radius and spend risk.
Show example snippet (optional)
onceonly.py
from onceonly import OnceOnly
import os
once = OnceOnly(api_key=os.environ["ONCEONLY_API_KEY"], fail_open=True)
# Stable idempotency key per real side-effect.
# Use a request id / job id / webhook delivery id / Stripe event id, etc.
event_id = "evt_..." # replace
key = f"stripe:webhook:{event_id}"
res = once.check_lock(key=key, ttl=3600)
if res.duplicate:
return {"status": "already_processed"}
# Safe to execute the side-effect exactly once.
handle_event(event_id)
When NOT to use: Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.
Fix reference: https://github.com/celery/celery/pull/6966
First fixed release: 5.2.0rc2
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not apply this fix if the CLI argument is intentionally set to False.
- Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.
Verify Fix
verify
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
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 |
|---|---|
| 5.2.0rc2 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.