Bagaimana Cara Mengatasi Error "Encountered two children with the same key" di React?

Saya punya function komponen bernama Users:

function Users() {
  const users = [
    { kelompok: 1, nama: 'Budi' },
    { kelompok: 1, nama: 'angga' },
  ];
  return (
    <ol>
      {users.map((user) => (
        <li key={user.kelompok}>{user.nama}</li>
      ))}
    </ol>
  );
}

Ketika saya jalankan muncul pesan kesalahan ini di browser:

Warning: Encountered two children with the same key, `1`. Keys should be unique so that components maintain their identity across updates. Non-unique keys may cause children to be duplicated and/or omitted — the behavior is unsupported and could change in a future version.
at ol
at Users
at div
at App 

Gimana cara mengatasinya ya?