Celery [5.3.0] Task results order is not preserved anymore

The Fix

pip install celery==5.3.4

Based on closed celery/celery issue #8421 · 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.

Jump to Verify Open PR/Commit

@@ -1704,7 +1704,7 @@ def _prepared(self, tasks, partial_args, group_id, root_id, app,
                 The generator yields tuples of the form ``(task, AsyncResult, group_id)``.
         """
-        for task in tasks:
+        for index, task in enumerate(tasks):
             if isinstance(task, CallableSignature):

repro.py

software -> celery:5.3.1 (emerald-rush) kombu:5.3.1 py:3.10.12
            billiard:4.1.0 py-amqp:5.1.1
platform -> system:Linux arch:64bit, ELF
            kernel version:6.1.30-0-virt imp:CPython
loader   -> celery.loaders.app.AppLoader
settings -> transport:amqp results:redis://redis:6379/

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==5.3.4\nWhen NOT to use: Do not apply this fix if task order is not a concern for your application.\n\n

Why This Fix Works in Production

Trigger: - [x] I have included all related issues and possible duplicate issues
Mechanism: The removal of a zip on results caused task results in a chord to not be received in order
Why the fix works: This fix addresses the issue where task results in a chord are not received in the same order as they were created by adding a group index when unrolling tasks. (first fixed release: 5.3.4).

Production impact:

If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).

Why This Breaks in Prod

The removal of a zip on results caused task results in a chord to not be received in order
Production symptom (often without a traceback): - [x] I have included all related issues and possible duplicate issues

Proof / Evidence

GitHub issue: #8421
Fix PR: https://github.com/celery/celery/pull/8427
First fixed release: 5.3.4
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.75
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.63

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“> Found a way to fix the issue while keeping all tests green: https://github.com/celery/celery/pull/8427”

@Nusnus · 2023-08-07 · confirmation · source

“you can come with a draft fix. we can help you along the way”

@auvipy · 2023-08-05 · source

“Found a way to fix the issue while keeping all tests green: https://github.com/celery/celery/pull/8427. Not sure at this point if this is a proper fix, so…”

@mkniewallner · 2023-08-07 · source

Failure Signature (Search String)

- [x] I have included all related issues and possible duplicate issues
async-timeout==4.0.2

Copy-friendly signature

signature.txt

Failure Signature
-----------------
- [x] I have included all related issues and possible duplicate issues
async-timeout==4.0.2

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
- [x] I have included all related issues and possible duplicate issues
async-timeout==4.0.2

Minimal Reproduction

repro.py

software -> celery:5.3.1 (emerald-rush) kombu:5.3.1 py:3.10.12
            billiard:4.1.0 py-amqp:5.1.1
platform -> system:Linux arch:64bit, ELF
            kernel version:6.1.30-0-virt imp:CPython
loader   -> celery.loaders.app.AppLoader
settings -> transport:amqp results:redis://redis:6379/

What Broke

Task results in a chord are received out of order, leading to incorrect processing.

Why It Broke

The removal of a zip on results caused task results in a chord to not be received in order

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install celery==5.3.4

When NOT to use: Do not apply this fix if task order is not a concern for your application.

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/8427

First fixed release: 5.3.4

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not apply this fix if task order is not a concern for your application.

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
5.3.4	Fixed

Related Issues

No related fixes found.

Cluster: celery:data-consistency Celery hub Celery best practices All hubs All clusters

Related clusters: Configuration error Duplicates Duplicate processing

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Celery [5.3.0] Task results order is not preserved anymore (Fix)