diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 5a3c6ef..1026403 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -30,6 +30,18 @@ jobs:
 
   pytest:
     runs-on: ubuntu-latest
+    name: pytest (${{ matrix.name }})
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - name: app
+            run: |
+              uv run alembic upgrade head
+              uv run pytest . --cov=. --cov-report xml
+          # pytest-alembic upgrades an empty database itself, so no `alembic upgrade` first.
+          - name: migrations
+            run: uv run pytest tests/migrations --override-ini=addopts=
     services:
       postgres:
         image: postgres:latest
@@ -52,8 +64,7 @@ jobs:
       - run: uv python pin 3.14
       - run: |
           uv sync --all-extras --all-groups --frozen --no-install-project
-          uv run alembic upgrade head
-          uv run pytest . --cov=. --cov-report xml
+          ${{ matrix.run }}
         env:
           SERVICE_ENVIRONMENT: ci
           PYTHONDONTWRITEBYTECODE: 1
diff --git a/AGENTS.md b/AGENTS.md
index c769ed6..43d5efa 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -13,6 +13,7 @@ The development workflow runs inside Docker via `just` (`just --list` / read the
 Things the recipe names don't make obvious:
 
 - `just test [args]` recreates a clean DB first (`alembic downgrade base` → `upgrade head`) and tears the stack down afterward; `[args]` are passed through to `pytest`.
+- `just test-migrations [args]` runs the `pytest-alembic` suite in `tests/migrations/` against an empty database: single head, upgrade, up/down consistency for every revision, and models matching the migrated schema (`alembic check` as a test). `just test` skips that directory (`--ignore` in `addopts`, `omit` in coverage) because it migrates the schema under the transaction-rollback fixture, so the recipe clears `addopts`.
 - `just run` applies migrations then starts the app on :8000.
 - `just lint` auto-fixes (eof-fixer + `ruff format` + `ruff check --fix` + `ty check`); CI (below) is the no-fix gate.
 
@@ -22,7 +23,7 @@ Running a single test (inside container or with DB available):
 uv run pytest tests/test_decks.py::test_get_decks -x
 ```
 
-CI (`.github/workflows/main.yml`) runs `ruff format --check`, `ruff check --no-fix`, `ty check`, then `alembic upgrade head` and `pytest` against a Postgres service. Match this locally before pushing.
+CI (`.github/workflows/main.yml`) runs `ruff format --check`, `ruff check --no-fix`, `ty check`, then two Postgres jobs: `alembic upgrade head` followed by `pytest`, and the `pytest-alembic` suite. Match this locally before pushing.
 
 ## Architecture
 
diff --git a/app/models.py b/app/models.py
index 3551f82..0e91826 100644
--- a/app/models.py
+++ b/app/models.py
@@ -27,4 +27,4 @@ class Card(BigIntAuditBase):
     front: orm.Mapped[str] = orm.mapped_column(sa.String, nullable=False)
     back: orm.Mapped[str | None] = orm.mapped_column(sa.String, nullable=True)
     hint: orm.Mapped[str | None] = orm.mapped_column(sa.String, nullable=True)
-    deck_id: orm.Mapped[int] = orm.mapped_column(sa.Integer, sa.ForeignKey("decks.id"))
+    deck_id: orm.Mapped[int] = orm.mapped_column(sa.BigInteger, sa.ForeignKey("decks.id"))
diff --git a/justfile b/justfile
index 9086db1..f950075 100644
--- a/justfile
+++ b/justfile
@@ -9,6 +9,9 @@ sh:
 test *args: down && down
     docker compose run application sh -c "sleep 1 && uv run alembic downgrade base && uv run alembic upgrade head && uv run pytest {{ args }}"
 
+test-migrations *args: down && down
+    docker compose run application sh -c "sleep 1 && uv run pytest tests/migrations --override-ini=addopts= {{ args }}"
+
 run:
     docker compose run --service-ports application sh -c "sleep 1 && uv run alembic upgrade head && uv run python -m app"
 
diff --git a/migrations/versions/2026-10-16_bigint_ids_and_required_deck_id.py b/migrations/versions/2026-10-16_bigint_ids_and_required_deck_id.py
new file mode 100644
index 0000000..57b90cd
--- /dev/null
+++ b/migrations/versions/2026-10-16_bigint_ids_and_required_deck_id.py
@@ -0,0 +1,33 @@
+"""bigint ids and required deck_id.
+
+Revision ID: 8e4a2c7b1f6d
+Revises: 5d1c0f3a9b2e
+Create Date: 2026-10-16 22:00:00.000000
+
+"""
+
+import sqlalchemy as sa
+from alembic import op
+
+
+# revision identifiers, used by Alembic.
+revision = "8e4a2c7b1f6d"
+down_revision = "5d1c0f3a9b2e"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.alter_column("decks", "id", type_=sa.BigInteger(), existing_type=sa.Integer(), existing_nullable=False)
+    op.execute("ALTER SEQUENCE decks_id_seq AS bigint")
+    op.alter_column("cards", "id", type_=sa.BigInteger(), existing_type=sa.Integer(), existing_nullable=False)
+    op.execute("ALTER SEQUENCE cards_id_seq AS bigint")
+    op.alter_column("cards", "deck_id", type_=sa.BigInteger(), existing_type=sa.Integer(), nullable=False)
+
+
+def downgrade() -> None:
+    op.alter_column("cards", "deck_id", type_=sa.Integer(), existing_type=sa.BigInteger(), nullable=True)
+    op.execute("ALTER SEQUENCE cards_id_seq AS integer")
+    op.alter_column("cards", "id", type_=sa.Integer(), existing_type=sa.BigInteger(), existing_nullable=False)
+    op.execute("ALTER SEQUENCE decks_id_seq AS integer")
+    op.alter_column("decks", "id", type_=sa.Integer(), existing_type=sa.BigInteger(), existing_nullable=False)
diff --git a/pyproject.toml b/pyproject.toml
index 3b9dc8c..6dd01bd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -33,6 +33,7 @@ dev = [
     "pytest-cov",
     "pytest-asyncio",
     "asgi_lifespan",
+    "pytest-alembic",
 ]
 lint = [
     "ruff",
@@ -79,7 +80,7 @@ isort.no-lines-before = ["standard-library", "local-folder"]
 ]
 
 [tool.pytest.ini_options]
-addopts = "--cov=. --cov-report term-missing --cov-fail-under=100"
+addopts = "--cov=. --cov-report term-missing --cov-fail-under=100 --ignore=tests/migrations"
 asyncio_mode = "auto"
 asyncio_default_fixture_loop_scope = "function"
 
@@ -90,3 +91,4 @@ exclude_also = [
 
 [tool.coverage.run]
 concurrency = ["thread", "greenlet"]
+omit = ["tests/migrations/*"]
diff --git a/tests/migrations/__init__.py b/tests/migrations/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/migrations/conftest.py b/tests/migrations/conftest.py
new file mode 100644
index 0000000..73e0992
--- /dev/null
+++ b/tests/migrations/conftest.py
@@ -0,0 +1,14 @@
+import typing
+
+import pytest
+from sqlalchemy import Engine, create_engine
+
+from app.settings import settings
+
+
+@pytest.fixture
+def alembic_engine() -> typing.Iterator[Engine]:
+    # Replaces pytest-alembic's default in-memory SQLite engine.
+    engine: typing.Final = create_engine(settings.db_dsn_parsed.set(drivername="postgresql+psycopg"))
+    yield engine
+    engine.dispose()
diff --git a/tests/migrations/test_migrations.py b/tests/migrations/test_migrations.py
new file mode 100644
index 0000000..1b937f7
--- /dev/null
+++ b/tests/migrations/test_migrations.py
@@ -0,0 +1,12 @@
+from pytest_alembic.tests import (
+    test_model_definitions_match_ddl,
+    test_single_head_revision,
+    test_up_down_consistency,
+    test_upgrade,
+)
+
+
+_ = test_single_head_revision
+_ = test_upgrade
+_ = test_model_definitions_match_ddl
+_ = test_up_down_consistency
diff --git a/uv.lock b/uv.lock
index 9788809..755638d 100644
--- a/uv.lock
+++ b/uv.lock
@@ -1,5 +1,5 @@
 version = 1
-revision = 3
+revision = 5
 requires-python = ">=3.14"
 
 [[package]]
@@ -281,6 +281,7 @@ dev = [
     { name = "httpx" },
     { name = "polyfactory" },
     { name = "pytest" },
+    { name = "pytest-alembic" },
     { name = "pytest-asyncio" },
     { name = "pytest-cov" },
 ]
@@ -312,6 +313,7 @@ dev = [
     { name = "httpx" },
     { name = "polyfactory" },
     { name = "pytest" },
+    { name = "pytest-alembic" },
     { name = "pytest-asyncio" },
     { name = "pytest-cov" },
 ]
@@ -977,6 +979,20 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/24/25/1de2678b631f5a49215c6c96fff41ba892b0a34df68d6d80292b1b48aa7f/pytest-9.1.1-py3-none-any.whl", hash = "sha256:37a86b45efb9a47a61a36449063e8e18d0cab3161329fc099eb21783169c4f0c", size = 386536, upload-time = "2026-06-19T10:58:31.347Z" },
 ]
 
+[[package]]
+name = "pytest-alembic"
+version = "0.13.1"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "alembic" },
+    { name = "pytest" },
+    { name = "sqlalchemy" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/00/99/272ace37071006a0050abf7b6940c6cfdcf58e18f27385be668f6a934ee0/pytest_alembic-0.13.1.tar.gz", hash = "sha256:96a54ec76d4704fffb433880c5a84f5c3ea5980bb3f6509d868fef40e6e9a79f", size = 39777, upload-time = "2026-10-02T16:21:52.261Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/5b/57/19e2e43140c04be1219f408fe840226c0f4d01550c9d5357f7ee6c86aa73/pytest_alembic-0.13.1-py3-none-any.whl", hash = "sha256:141b410c2d338d98401981dc4f8a848ea46c2c5c46dae106f1bcbed33dccdc47", size = 46278, upload-time = "2026-10-02T16:21:51.261Z" },
+]
+
 [[package]]
 name = "pytest-asyncio"
 version = "1.4.0"