Votes cast in the 2014 local elections for Listowel, Co. Kerry will have to be counted again following a Supreme Court ruling.
Former Senator Dan Kiely challenged the result after losing out on a seat on Kerry County Council by just two votes.
The court agreed that inferring a first preference on ballot cards where only the numbers 3, 4 and 5 were used was a mistake.
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All five judges agreed it rendered the outcome unlawful, while four of the five ruled there should be a recount.
Mr Kiely lost a close race for the final seat in the constituency in the 2014 election.