diff --git a/app/api/cards.py b/app/api/cards.py
index 36f08cd..6063c5f 100644
--- a/app/api/cards.py
+++ b/app/api/cards.py
@@ -41,7 +41,7 @@ async def create_cards(
 @ROUTER.put("/decks/{deck_id}/cards/")
 async def update_cards(
     deck_id: int,
-    data: list[schemas.Card],
+    data: list[schemas.CardUpdate],
     update_cards_use_case: UpdateCardsUseCase = FromDI(UpdateCardsUseCase),
 ) -> schemas.Cards:
     return schemas.Cards.from_models(await update_cards_use_case(deck_id=deck_id, data=data))
diff --git a/app/repositories.py b/app/repositories.py
index 1e2f7e5..9accdc1 100644
--- a/app/repositories.py
+++ b/app/repositories.py
@@ -49,8 +49,8 @@ async def list_for_deck(self, deck_id: int) -> Sequence[models.Card]:
     async def add_cards(self, deck_id: int, cards: list[schemas.CardCreate]) -> Sequence[models.Card]:
         return await self.create_many([models.Card(**card.model_dump(), deck_id=deck_id) for card in cards])
 
-    async def upsert_cards(self, deck_id: int, cards: list[schemas.Card]) -> Sequence[models.Card]:
+    async def upsert_cards(self, deck_id: int, cards: list[schemas.CardUpdate]) -> Sequence[models.Card]:
         upserted = await self.upsert_many(
-            [models.Card(**card.model_dump(exclude={"deck_id"}), deck_id=deck_id) for card in cards],
+            [models.Card(**card.model_dump(), deck_id=deck_id) for card in cards],
         )
         return sorted(upserted, key=operator.attrgetter("id"))
diff --git a/app/schemas.py b/app/schemas.py
index 42a7fc5..f59a8a4 100644
--- a/app/schemas.py
+++ b/app/schemas.py
@@ -31,9 +31,12 @@ class CardCreate(CardBase):
     pass
 
 
-class Card(CardBase):
+class CardUpdate(CardBase):
     id: PositiveInt
-    deck_id: PositiveInt | None = None
+
+
+class Card(CardUpdate):
+    deck_id: PositiveInt
 
 
 class Cards(Collection[Card]):
diff --git a/app/use_cases/update_cards.py b/app/use_cases/update_cards.py
index 6a6774c..291a893 100644
--- a/app/use_cases/update_cards.py
+++ b/app/use_cases/update_cards.py
@@ -14,7 +14,7 @@ class UpdateCardsUseCase:
     cards_repository: CardsRepository
 
     @postgres_retry
-    async def __call__(self, *, deck_id: int, data: list[schemas.Card]) -> Sequence[models.Card]:
+    async def __call__(self, *, deck_id: int, data: list[schemas.CardUpdate]) -> Sequence[models.Card]:
         async with self.transaction:
             cards: typing.Final = await self.cards_repository.upsert_cards(deck_id, data)
             await self.transaction.commit()
diff --git a/tests/test_cards.py b/tests/test_cards.py
index 2118284..6c0d876 100644
--- a/tests/test_cards.py
+++ b/tests/test_cards.py
@@ -135,3 +135,11 @@ async def test_cards_ordered_by_id_after_update(client: AsyncClient) -> None:
     response = await client.get(f"/api/decks/{deck.id}/cards/")
     assert response.status_code == status.HTTP_200_OK
     assert [x["id"] for x in response.json()["items"]] == [card1.id, card2.id]
+
+
+async def test_openapi_card_deck_id_required(client: AsyncClient) -> None:
+    response = await client.get("/openapi.json")
+    assert response.status_code == status.HTTP_200_OK
+    card_schema = response.json()["components"]["schemas"]["Card"]
+    assert "deck_id" in card_schema["required"]
+    assert "null" not in {x.get("type") for x in card_schema["properties"]["deck_id"].get("anyOf", [])}