diff --git a/backend/tests/test_registration.py b/backend/tests/test_registration.py
index 9d1b864e..c30629aa 100644
--- a/backend/tests/test_registration.py
+++ b/backend/tests/test_registration.py
@@ -4,9 +4,9 @@ from cryptography.hazmat.primitives.ciphers.aead import AESGCM
 from cryptography.hazmat.primitives import hashes, serialization
 from cryptography.hazmat.primitives.asymmetric import padding
 from httpx import AsyncClient
-from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy import UUID as SA_UUID, select
+from sqlalchemy.dialects.postgresql import UUID as PG_UUID
 from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
-from sqlalchemy.ext.compiler import compiles
 import base64
 import json
 import os
@@ -15,16 +15,15 @@ from app.main import create_app
 from app.core.deps import get_db_session
 from app.core.security import hash_password
 from app.crud import user as user_crud
+from app.db.base_class import Base
+from tests.conftest import GUID
+from app.models.study_member import StudyMember
 from app.models.user import User, UserRole, UserStatus
+from app.schemas.user import UserRegisterRequest
 
 TEST_DATABASE_URL = "sqlite+aiosqlite:///:memory:"
 
 
-@compiles(UUID, "sqlite")
-def compile_uuid_for_sqlite(_type, _compiler, **_kw):
-    return "CHAR(32)"
-
-
 async def encrypted_auth_payload(client: AsyncClient, email: str, password: str) -> dict:
     key_resp = await client.get("/api/v1/auth/login-key")
     assert key_resp.status_code == 200
@@ -73,32 +72,44 @@ async def encrypted_login(client: AsyncClient, email: str, password: str):
 async def client_and_db():
     engine = create_async_engine(TEST_DATABASE_URL, future=True)
     TestSessionLocal = async_sessionmaker(engine, expire_on_commit=False)
-    async with engine.begin() as conn:
-        await conn.run_sync(User.__table__.create)
+    original_column_types = {
+        column: column.type
+        for table in Base.metadata.tables.values()
+        for column in table.columns
+    }
+    for table in Base.metadata.tables.values():
+        for column in table.columns:
+            if isinstance(column.type, (PG_UUID, SA_UUID)):
+                column.type = GUID()
+    try:
+        async with engine.begin() as conn:
+            await conn.run_sync(Base.metadata.create_all)
+
+        async def override_get_db():
+            async with TestSessionLocal() as session:
+                yield session
+
+        app = create_app()
+        app.dependency_overrides[get_db_session] = override_get_db
 
-    async def override_get_db():
         async with TestSessionLocal() as session:
-            yield session
+            admin = User(
+                email="admin@test.com",
+                password_hash=hash_password("admin123"),
+                full_name="Admin",
+                clinical_department="Admin",
+                role=UserRole.ADMIN,
+                status=UserStatus.ACTIVE,
+            )
+            session.add(admin)
+            await session.commit()
 
-    app = create_app()
-    app.dependency_overrides[get_db_session] = override_get_db
-
-    async with TestSessionLocal() as session:
-        admin = User(
-            email="admin@test.com",
-            password_hash=hash_password("admin123"),
-            full_name="Admin",
-            clinical_department="Admin",
-            role=UserRole.ADMIN,
-            status=UserStatus.ACTIVE,
-        )
-        session.add(admin)
-        await session.commit()
-
-    async with AsyncClient(app=app, base_url="http://test") as client:
-        yield client, TestSessionLocal
-
-    await engine.dispose()
+        async with AsyncClient(app=app, base_url="http://test") as client:
+            yield client, TestSessionLocal
+    finally:
+        for column, original_type in original_column_types.items():
+            column.type = original_type
+        await engine.dispose()
 
 
 @pytest.mark.asyncio
@@ -108,7 +119,6 @@ async def test_register_creates_pending_user(client_and_db):
         "email": "newuser@test.com",
         "password": "Password123",
         "full_name": "New User",
-        "role": "CRA",
         "clinical_department": "Clinical",
     }
     resp = await client.post("/api/v1/auth/register", json=payload)
@@ -117,6 +127,11 @@ async def test_register_creates_pending_user(client_and_db):
         user = await user_crud.get_by_email(session, payload["email"])
         assert user is not None
         assert user.status == UserStatus.PENDING
+        assert user.role == UserRole.PV
+        member_rows = (
+            await session.execute(select(StudyMember).where(StudyMember.user_id == user.id))
+        ).scalars().all()
+        assert member_rows == []
 
 
 @pytest.mark.asyncio
@@ -140,7 +155,6 @@ async def test_login_blocked_before_approval(client_and_db):
         "email": "pending@test.com",
         "password": "Password123",
         "full_name": "Pending User",
-        "role": "PV",
         "clinical_department": "Safety",
     }
     await client.post("/api/v1/auth/register", json=payload)
@@ -156,7 +170,6 @@ async def test_admin_can_approve_user(client_and_db):
         "email": "approve@test.com",
         "password": "Password123",
         "full_name": "Approve Target",
-        "role": "IMP",
         "clinical_department": "Supply",
     }
     await client.post("/api/v1/auth/register", json=payload)
@@ -176,18 +189,8 @@ async def test_admin_can_approve_user(client_and_db):
         assert refreshed.approved_by is not None
 
 
-@pytest.mark.asyncio
-async def test_admin_role_cannot_register(client_and_db):
-    client, _ = client_and_db
-    payload = {
-        "email": "admin-register@test.com",
-        "password": "Password123",
-        "full_name": "Bad Admin",
-        "role": "ADMIN",
-        "clinical_department": "IT",
-    }
-    resp = await client.post("/api/v1/auth/register", json=payload)
-    assert resp.status_code in (400, 422)
+def test_register_request_does_not_expose_role_input():
+    assert "role" not in UserRegisterRequest.model_fields
 
 
 @pytest.mark.asyncio