def calculate_custom_fields_support(custom_fields):
    """
    Return a dictionary of `{field_id: set(profiles_that_don't_support_it)}`.
    `custom_fields` should be of the form: {profile_id: [field_definition, ...], ...}
    """
    all_profiles = set(custom_fields.keys())
    custom_fields_sets = {}
    for fields in custom_fields.values():
        for field in fields:
            custom_fields_sets[field['id']] = custom_fields_sets.get(field[
                'id'], all_profiles) - set(field['profiles'])
    return custom_fields_sets
