def add_ago_to_since(since: str) ->str:
    """
    Backwards compatibility hack. Without this slices with since: 7 days will
    be treated as 7 days in the future.

    :param str since:
    :returns: Since with ago added if necessary
    :rtype: str
    """
    since_words = since.split(' ')
    grains = ['days', 'years', 'hours', 'day', 'year', 'weeks']
    if len(since_words) == 2 and since_words[1] in grains:
        since += ' ago'
    return since
