The Fix
pip install celery==4.4.7
Based on closed celery/celery issue #6258 · 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.
@@ -276,3 +276,4 @@ Arel Cordero, 2019/08/29
Dipankar Achinta, 2019/10/24
Sardorbek Imomaliev, 2020/01/24
+Maksym Shalenyi, 2020/07/30
diff --git a/celery/backends/mongodb.py b/celery/backends/mongodb.py
index f7474a189b4..17cb4f846ba 100644
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==4.4.7\nWhen NOT to use: Do not apply this fix if using a different result backend.\n\n
Why This Fix Works in Production
- Trigger: - [x] I have included all related issues and possible duplicate issues
- Mechanism: The serialization logic in the MongoDB result backend was incorrectly implemented
- Why the fix works: Fixed serialization issue in MongoDB result backend. (first fixed release: 4.4.7).
- 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
- The serialization logic in the MongoDB result backend was incorrectly implemented
- Production symptom (often without a traceback): - [x] I have included all related issues and possible duplicate issues
Proof / Evidence
- GitHub issue: #6258
- Fix PR: https://github.com/celery/celery/pull/6259
- First fixed release: 4.4.7
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.75
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.70
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“<!-- Please fill this template entirely and do not erase parts of it. We reserve the right to close without a response bug reports which are incomplete. --> # Checklist <!-- To check an item on the list replace [ ] with [x]. --> - [x] I hav”
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
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 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
- this bug.
What Broke
Tasks failed to serialize results correctly, leading to data retrieval issues.
Why It Broke
The serialization logic in the MongoDB result backend was incorrectly implemented
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install celery==4.4.7
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/6259
First fixed release: 4.4.7
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not apply this fix if using a different result backend.
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 |
|---|---|
| 4.4.7 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.