The regulator of the National Lottery says €16m in expired unclaimed prizes is being returned to the State.
This follows an agreement with the current lottery operator, Premier Lotteries Ireland.
The money, which dates back to the end of the previous licence held by An Post, will be returned to the Exchequer for the benefit of National Lottery good causes.
The money relates to prizes not claimed by winners by the ticket expiry date.
The 2014 licence did not explicitly state what should happen to this money as the National Lottery transitioned to the new licence.
But the issue has now been resolved by an amendment following a review by the regulator.
The amendment covers 'Historical Expired Unclaimed Prizes', or HEUP, of €16,091,653.
Carol Boate is regulator of the National Lottery.
She said: "Following thorough consideration of the matter I had concluded that there was no basis for the money to be used by the current operator.
"This agreement with the operator now means the money can be returned to the Exchequer without delay for use by good causes, further ensuring that funds for this purpose are maximised at this time."