diff --git a/src/parallel/_models.py b/src/parallel/_models.py
index 8c5ab26..20b77a7 100644
--- a/src/parallel/_models.py
+++ b/src/parallel/_models.py
@@ -1,6 +1,8 @@
 from __future__ import annotations
 
 import os
+import sys
+import types
 import inspect
 import weakref
 from typing import (
@@ -687,6 +689,15 @@ class CachedDiscriminatorType(Protocol):
 DISCRIMINATOR_CACHE: weakref.WeakKeyDictionary[type, DiscriminatorDetails] = weakref.WeakKeyDictionary()
 
 
+def _discriminator_cache_key(union: type) -> type:
+    union_type = cast(Optional[type[object]], getattr(types, "UnionType", None))
+    if (3, 10) <= sys.version_info < (3, 14) and union_type is not None and isinstance(union, union_type):
+        # PEP 604 unions cannot be weakly referenced before Python 3.14. The
+        # equivalent typing.Union can still serve as a weak cache key.
+        return cast(type, cast(Any, Union)[get_args(union)])
+    return union
+
+
 class DiscriminatorDetails:
     field_name: str
     """The name of the discriminator field in the variant class, e.g.
@@ -729,7 +740,8 @@ def __init__(
 
 
 def _build_discriminated_union_meta(*, union: type, meta_annotations: tuple[Any, ...]) -> DiscriminatorDetails | None:
-    cached = DISCRIMINATOR_CACHE.get(union)
+    key = _discriminator_cache_key(union)
+    cached = DISCRIMINATOR_CACHE.get(key)
     if cached is not None:
         return cached
 
@@ -784,7 +796,7 @@ def _build_discriminated_union_meta(*, union: type, meta_annotations: tuple[Any,
         discriminator_field=discriminator_field_name,
         discriminator_alias=discriminator_alias,
     )
-    DISCRIMINATOR_CACHE.setdefault(union, details)
+    DISCRIMINATOR_CACHE.setdefault(key, details)
     return details
 
 
diff --git a/tests/test_models.py b/tests/test_models.py
index 12db0ec..5303f1b 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -1,3 +1,4 @@
+import sys
 import json
 from typing import TYPE_CHECKING, Any, Dict, List, Union, Iterable, Optional, cast
 from datetime import datetime, timezone
@@ -834,6 +835,63 @@ class B(BaseModel):
     assert DISCRIMINATOR_CACHE.get(UnionType) is discriminator
 
 
+@pytest.mark.skipif(sys.version_info < (3, 10), reason="PEP 604 unions require Python 3.10")
+def test_pep604_union_invalid_data() -> None:
+    class A(BaseModel):
+        type: Literal["a"]
+
+        data: str
+
+    class B(BaseModel):
+        type: Literal["b"]
+
+        data: int
+
+    PEP604Union = cast(Any, A).__or__(B).__or__(type(None))
+    m = construct_type(value={"type": "b", "data": "foo"}, type_=PEP604Union)
+
+    assert isinstance(m, A)
+    assert m.type == "b"  # type: ignore[comparison-overlap]
+    assert m.data == "foo"
+
+
+@pytest.mark.skipif(sys.version_info < (3, 10), reason="PEP 604 unions require Python 3.10")
+def test_discriminated_pep604_union_invalid_data_uses_cache() -> None:
+    class A(BaseModel):
+        type: Literal["a"]
+
+        data: str
+
+    class B(BaseModel):
+        type: Literal["b"]
+
+        data: int
+
+    UnionType = cast(Any, Union[A, B, None])
+    PEP604Union = cast(Any, A).__or__(B).__or__(type(None))
+
+    assert not DISCRIMINATOR_CACHE.get(UnionType)
+
+    m = construct_type(
+        value={"type": "b", "data": "foo"},
+        type_=cast(Any, Annotated[PEP604Union, PropertyInfo(discriminator="type")]),
+    )
+    assert isinstance(m, B)
+    assert m.type == "b"
+    assert m.data == "foo"  # type: ignore[comparison-overlap]
+
+    discriminator = DISCRIMINATOR_CACHE.get(UnionType)
+    assert discriminator is not None
+
+    m = construct_type(
+        value={"type": "b", "data": "bar"},
+        type_=cast(Any, Annotated[PEP604Union, PropertyInfo(discriminator="type")]),
+    )
+    assert isinstance(m, B)
+    assert m.data == "bar"  # type: ignore[comparison-overlap]
+    assert DISCRIMINATOR_CACHE.get(UnionType) is discriminator
+
+
 @pytest.mark.skipif(PYDANTIC_V1, reason="TypeAliasType is not supported in Pydantic v1")
 def test_type_alias_type() -> None:
     Alias = TypeAliasType("Alias", str)  # pyright: ignore