diff --git a/backend/app/api/routes/auth.py b/backend/app/api/routes/auth.py
index 012bd8b..ff9b41e 100644
--- a/backend/app/api/routes/auth.py
+++ b/backend/app/api/routes/auth.py
@@ -30,7 +30,7 @@ def register(body: RegisterRequest, db: Session = Depends(get_db)):
 
     if body.invite_token:
         invite = db.query(InviteToken).filter(InviteToken.token == body.invite_token).first()
-        if not invite or invite.used_by or invite.expires_at < datetime.now():
+        if not invite or invite.used_by or invite.expires_at < datetime.now(UTC).replace(tzinfo=None):
             raise HTTPException(status_code=400, detail="Invalid or expired invite")
         if invite.email and invite.email.lower() != body.email.lower():
             raise HTTPException(status_code=400, detail="Email does not match invite")
@@ -46,10 +46,11 @@ def register(body: RegisterRequest, db: Session = Depends(get_db)):
         role=role,
     )
     db.add(user)
+    db.flush()
 
     if invite:
         invite.used_by = user.id
-        invite.used_at = datetime.now(UTC)
+        invite.used_at = datetime.now(UTC).replace(tzinfo=None)
 
     db.commit()
     db.refresh(user)
diff --git a/backend/app/api/routes/invites.py b/backend/app/api/routes/invites.py
index e2e5dd2..b377b83 100644
--- a/backend/app/api/routes/invites.py
+++ b/backend/app/api/routes/invites.py
@@ -25,7 +25,7 @@ def create_invite(
         email=body.email,
         role=body.role,
         created_by=current_user.id,
-        expires_at=datetime.now(UTC) + timedelta(days=7),
+        expires_at=datetime.now(UTC).replace(tzinfo=None) + timedelta(days=7),
     )
     db.add(invite)
     db.commit()
@@ -61,6 +61,6 @@ def delete_invite(
 @router.get("/{token}/validate")
 def validate_invite(token: str, db: Session = Depends(get_db)):
     invite = db.query(InviteToken).filter(InviteToken.token == token).first()
-    if not invite or invite.used_by or invite.expires_at < datetime.now(UTC):
+    if not invite or invite.used_by or invite.expires_at < datetime.now(UTC).replace(tzinfo=None):
         return {"valid": False}
     return {"valid": True, "email": invite.email, "role": invite.role}
diff --git a/backend/tests/test_invites.py b/backend/tests/test_invites.py
new file mode 100644
index 0000000..eadb5e0
--- /dev/null
+++ b/backend/tests/test_invites.py
@@ -0,0 +1,114 @@
+def test_create_invite(client, auth_header):
+    resp = client.post(
+        "/api/invites",
+        json={"email": "newuser@example.com", "role": "member"},
+        headers=auth_header,
+    )
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["token"]
+    assert data["email"] == "newuser@example.com"
+    assert data["role"] == "member"
+    assert data["used_at"] is None
+
+
+def test_create_invite_without_email(client, auth_header):
+    resp = client.post(
+        "/api/invites",
+        json={"role": "admin"},
+        headers=auth_header,
+    )
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["email"] is None
+    assert data["role"] == "admin"
+
+
+def test_create_invite_requires_admin(client):
+    client.post(
+        "/api/auth/register",
+        json={"email": "first@example.com", "password": "password123", "name": "First"},
+    )
+    invite_resp = client.post(
+        "/api/invites",
+        json={"email": "new@example.com", "role": "member"},
+        headers={"Authorization": "Bearer first_token"},
+    )
+    assert invite_resp.status_code == 401
+
+
+def test_validate_invite(client, auth_header):
+    create_resp = client.post(
+        "/api/invites",
+        json={"email": "newuser@example.com", "role": "member"},
+        headers=auth_header,
+    )
+    token = create_resp.json()["token"]
+
+    validate_resp = client.get(f"/api/invites/{token}/validate")
+    assert validate_resp.status_code == 200
+    data = validate_resp.json()
+    assert data["valid"] is True
+    assert data["email"] == "newuser@example.com"
+    assert data["role"] == "member"
+
+
+def test_validate_invalid_token(client):
+    resp = client.get("/api/invites/nonexistent-token/validate")
+    assert resp.status_code == 200
+    assert resp.json()["valid"] is False
+
+
+def test_list_invites(client, auth_header):
+    client.post(
+        "/api/invites",
+        json={"email": "a@example.com"},
+        headers=auth_header,
+    )
+    client.post(
+        "/api/invites",
+        json={"email": "b@example.com"},
+        headers=auth_header,
+    )
+    resp = client.get("/api/invites", headers=auth_header)
+    assert resp.status_code == 200
+    assert len(resp.json()) == 2
+
+
+def test_delete_invite(client, auth_header):
+    create_resp = client.post(
+        "/api/invites",
+        json={"email": "delete@example.com"},
+        headers=auth_header,
+    )
+    invite_id = create_resp.json()["id"]
+
+    delete_resp = client.delete(f"/api/invites/{invite_id}", headers=auth_header)
+    assert delete_resp.status_code == 200
+
+    list_resp = client.get("/api/invites", headers=auth_header)
+    assert len(list_resp.json()) == 0
+
+
+def test_register_with_invite(client, auth_header):
+    create_resp = client.post(
+        "/api/invites",
+        json={"email": "invited@example.com", "role": "member"},
+        headers=auth_header,
+    )
+    token = create_resp.json()["token"]
+
+    reg_resp = client.post(
+        "/api/auth/register",
+        json={
+            "email": "invited@example.com",
+            "password": "password123",
+            "name": "Invited User",
+            "invite_token": token,
+        },
+    )
+    assert reg_resp.status_code == 200
+    assert "access_token" in reg_resp.json()
+
+    validate_resp = client.get(f"/api/invites/{token}/validate")
+    assert validate_resp.json()["valid"] is False