def make_header_id_unique(header_id, used_ids):
    """Make the given ID unique given a dictionary of used_ids

    Arguments:
    header_id - Slugified header ID
    used_id - Dictionary associating each header ID without suffixes to 
    the number of times that such ID has been used.
    """
    if header_id in used_ids:
        unique_header_id = header_id + '-' + str(used_ids[header_id])
        used_ids[header_id] += 1
    else:
        unique_header_id = header_id
        used_ids[header_id] = 1

    return unique_header_id