The Fix
pip install celery==5.3.0b2
Based on closed celery/celery issue #7855 · 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.
@@ -453,8 +453,7 @@ them into the Kombu serializer registry
json -- JSON is supported in many programming languages, is now
- a standard part of Python (since 2.6), and is fairly fast to decode
- using the modern Python libraries, such as :pypi:`simplejson`.
+ a standard part of Python (since 2.6), and is fairly fast to decode.
Option A — Upgrade to fixed release\npip install celery==5.3.0b2\nWhen NOT to use: This fix should not be applied if the documentation is still accurate or if the msgpack format is not used.\n\n
Why This Fix Works in Production
- Trigger: - [x] I have included all related issues and possible duplicate issues in this issue
- Mechanism: The serialization documentation contained outdated warnings about msgpack being experimental
- Why the fix works: Updates the serialization documentation to remove outdated warnings and provide installation instructions for serializer libraries. (first fixed release: 5.3.0b2).
- If left unfixed, retries/timeouts can trigger duplicate external side-effects (double charges, duplicate emails, repeated writes).
Why This Breaks in Prod
- The serialization documentation contained outdated warnings about msgpack being experimental
- Production symptom (often without a traceback): - [x] I have included all related issues and possible duplicate issues in this issue
Proof / Evidence
- GitHub issue: #7855
- Fix PR: https://github.com/celery/celery/pull/7858
- First fixed release: 5.3.0b2
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.75
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.69
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Hey @sondrelg :wave:, Thank you for opening an issue”
“I think these should probably also mention that accept_content needs to be expanded for other serialization formats to work. Otherwise you'll see discarded tasks #6953…”
Failure Signature (Search String)
- - [x] I have included all related issues and possible duplicate issues in this issue
- or possible duplicates to this issue as requested by the checklist above.
Copy-friendly signature
Failure Signature
-----------------
- [x] I have included all related issues and possible duplicate issues in this issue
or possible duplicates to this issue as requested by the checklist above.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
- [x] I have included all related issues and possible duplicate issues in this issue
or possible duplicates to this issue as requested by the checklist above.
What Broke
Users may encounter confusion or misconfiguration due to outdated documentation.
Why It Broke
The serialization documentation contained outdated warnings about msgpack being experimental
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install celery==5.3.0b2
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/7858
First fixed release: 5.3.0b2
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix should not be applied if the documentation is still accurate or if the msgpack format is not used.
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 |
|---|---|
| 5.3.0b2 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.