(How) can I use the [Range] attribute on a [Serializable] class?

I have a class

public class Example : MonoBehavior {

    [Serializable]
    public class SubExample {
        [SerializeField]
        [Range(1,6)]
        private int _Count;
    }

    [SerializeField]
    private List<SubExample> _exampleList;

    [SerializeField]
    [Range(1,6)]
    private int _testRange;
}

In the inspector anyway only the _testRange is displayed as Range while the _Count of the elements of _exampleList are only shown as number.

Am I missing something to get the Range behavior also on the variables in serializable elements of the list?

It works just fine for me. What version of unity are you in? do you have any compilation errors? did the script get saved before you let it recompile?