Pydantic Enums with `NamedTuple` values not supported (Fix)

The Fix

pip install pydantic==2.12.5

Based on closed pydantic/pydantic issue #12503 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -1110,6 +1110,10 @@ def match_type(self, obj: Any) -> core_schema.CoreSchema:  # noqa: C901
         elif is_typeddict(obj):
             return self._typed_dict_schema(obj, None)
+        elif inspect.isclass(obj) and issubclass(obj, Enum):
+            # NOTE: this must come before the `is_namedtuple()` check as enums values
+            # can be namedtuples:

repro.py

# src/test.py
from enum import Enum
from typing import NamedTuple
from pydantic import BaseModel


class _Something(NamedTuple):
    content: str


class MyEnum(_Something, Enum):
    FOO = "foo"


class MyModel(BaseModel):
    s: MyEnum


MyModel(s=MyEnum.FOO)

verify

Re-run: python src/test.py

fix.md

Option A — Upgrade to fixed release\npip install pydantic==2.12.5\nWhen NOT to use: This fix should not be used if the Enum does not derive from NamedTuple.\n\n

Why This Fix Works in Production

Trigger: $ python src/test.py
Mechanism: Pydantic rejected instances of Enum with NamedTuple values due to type matching issues
Why the fix works: Fix support for enums with NamedTuple as values, resolving the issue where Pydantic rejected instances of the Enum as valid values. (first fixed release: 2.12.5).

Production impact:

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

Why This Breaks in Prod

Shows up under Python 3.13 in real deployments (not just unit tests).
Pydantic rejected instances of Enum with NamedTuple values due to type matching issues
Surfaces as: $ python src/test.py

Proof / Evidence

GitHub issue: #12503
Fix PR: https://github.com/pydantic/pydantic/pull/12506
First fixed release: 2.12.5
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.46

Discussion

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

Jump to Sources Open on GitHub

“### Initial Checks - [x] I confirm that I'm using Pydantic V2 ### Description I am using a custom class as branches of an Enum; And I would like to specify a model's property to be of type this Enum. However, pydantic rejects instances of t”

Issue thread · issue description · source

Failure Signature (Search String)

$ python src/test.py

Error Message

Stack trace

error.txt

Error Message
-------------
$ python src/test.py 
Traceback (most recent call last):
  File "/app/src/yolo.py", line 18, in <module>
    MyModel(s=MyEnum.FOO)
    ~~~~~~~^^^^^^^^^^^^^^
  File "/app/.venv/lib/python3.13/site-packages/pydantic/main.py", line 253, in __init__
    validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
  File "/usr/local/lib/python3.13/enum.py", line 726, in __call__
    return cls.__new__(cls, value)
           ~~~~~~~~~~~^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/enum.py", line 1203, in __new__
    raise ve_exc
ValueError: 'foo' is not a valid MyEnum

Minimal Reproduction

repro.py

# src/test.py
from enum import Enum
from typing import NamedTuple
from pydantic import BaseModel


class _Something(NamedTuple):
    content: str


class MyEnum(_Something, Enum):
    FOO = "foo"


class MyModel(BaseModel):
    s: MyEnum


MyModel(s=MyEnum.FOO)

Environment

Python: 3.13
Pydantic: 2

What Broke

Instances of Enum were not accepted, causing validation errors in models.

Why It Broke

Pydantic rejected instances of Enum with NamedTuple values due to type matching issues

Fix Options (Details)

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

pip install pydantic==2.12.5

When NOT to use: This fix should not be used if the Enum does not derive from NamedTuple.

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

Fix reference: https://github.com/pydantic/pydantic/pull/12506

First fixed release: 2.12.5

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

When NOT to Use This Fix

This fix should not be used if the Enum does not derive from NamedTuple.

Verify Fix

verify

Re-run: python src/test.py

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.

Version Compatibility Table

Version	Status
2.12.5	Fixed

Related Issues

No related fixes found.

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Related clusters: Configuration error OpenAPI schema Serialization

Sources

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