Celery Task.retry() always raises RuntimeError if

The Fix

pip install celery==4.4.3

Based on closed celery/celery issue #4661 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -709,15 +709,14 @@ def retry(self, args=None, kwargs=None, exc=None, throw=True,
             )
 
-        ret = Retry(exc=exc, when=eta or countdown)
+        ret = Retry(exc=exc, when=eta or countdown, is_eager=is_eager, sig=S)

repro.py

from unittest import mock

with mock.patch(
    'celery.app.task.denied_join_result'
) as mocked_task_join_will_block:
    mocked_task_join_will_block.__enter__.return_value = None

    # run your task as you wish...

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==4.4.3\nWhen NOT to use: This fix should not be used if eager execution is not intended.\n\nOption C — Workaround\nwith mock that allows you to run your tests on version `4.3.x`\nWhen NOT to use: This fix should not be used if eager execution is not intended.\n\n

Why This Fix Works in Production

Mechanism: Changes the eager retry behavior in Celery, allowing tasks to return the eventual value or MaxRetriesExceededError when using self.retry.
Why the fix works: Changes the eager retry behavior in Celery, allowing tasks to return the eventual value or MaxRetriesExceededError when using self.retry. (first fixed release: 4.4.3).

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

Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #4661
Fix PR: https://github.com/celery/celery/pull/6109
First fixed release: 4.4.3
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.58

Discussion

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

Jump to Sources Open on GitHub

“This PR https://github.com/celery/celery/pull/6109 resolves this issue as well.”

@fazlerabby7 · 2020-05-22 · confirmation · source

“since this is marked with the 4.3 milestone, I want to note that this still happens with 4.3. Please let me know if you require…”

@untitaker · 2019-04-07 · repro detail · source

“I had the same issue, but I only use always_eager for tests. I made a workaround with mock that allows you to run your tests…”

@jarussi · 2019-08-05 · source

“Inspired by @jarussi you can simplify the workaround to: Now you can apply it to the entire test case in one shot. The __enter__ lookup…”

@hedleyroos · 2020-01-20 · source

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
    ...
    raise RuntimeError(E_WOULDBLOCK)
RuntimeError: Never call result.get() within a task!
See http://docs.celeryq.org/en/latest/userguide/tasks.html#task-synchronous-subtasks

Minimal Reproduction

repro.py

from unittest import mock

with mock.patch(
    'celery.app.task.denied_join_result'
) as mocked_task_join_will_block:
    mocked_task_join_will_block.__enter__.return_value = None

    # run your task as you wish...

What Broke

Tasks fail to retry, causing unexpected task failures in production environments.

Fix Options (Details)

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

pip install celery==4.4.3

When NOT to use: This fix should not be used if eager execution is not intended.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Option C — Workaround Temporary workaround

with mock that allows you to run your tests on version `4.3.x`

When NOT to use: This fix should not be used if eager execution is not intended.

Use only if you cannot change versions today. Treat this as a stopgap and remove once upgraded.

Fix reference: https://github.com/celery/celery/pull/6109

First fixed release: 4.4.3

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

When NOT to Use This Fix

This fix should not be used if eager execution is not intended.

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

Make timeouts explicit and test them (unit + integration) to avoid silent behavior changes.
Instrument retries (attempt count + reason) and alert on spikes to catch dependency slowdowns.

Version Compatibility Table

Version	Status
4.4.3	Fixed

Related Issues

No related fixes found.

Cluster: celery:configuration-error Celery hub Celery best practices All hubs All clusters

Related clusters: Data consistency Duplicates Duplicate processing

Sources

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

Celery Task.retry() always raises RuntimeError if task_always_eager and task_eager_propagates are (Fix)