The Catholic Church will move St Patrick's Day 2008 after discovering it clashes with a key day in the Church's calendar.
Bishops discovered the Irish patron saint's feast on March 17 clashes with the second day of Holy Week next year.
Church rules decree the saint's feast day does not rank as highly as the Monday before Easter and therefore has to be moved.
Fr Peter Jones, of the Liturgy Commission, insisted the move was necessary. He said: "It's about the religious aspect of the feast and mass on the day.
"It's about the Holy Day which can't be observed on the Monday of Holy Week and therefore has to be transferred in accordance with the usual rules."
Rome approved the shift of the official religious celebration two days back to March 15, which falls on a Saturday.
The celebration should have been moved to the next available day in the Church's calendar, April 1, but senior Irish clerics wanted to keep the date as close to international civic celebrations as possible, as they are planned years in advance.
The last time St Patrick's Day had to be moved was in 1940 when it coincided with Palm Sunday, the first day of Holy Week. The next date it will have to be moved again is 2160.
Sinead Grace, of Tourism Ireland, said the traditional St Patrick's Day parade through Dublin has now become a week-long festival.
"I wouldn't imagine too many people are aware of the religious aspect. I can't see that it will make any difference to the bookings of hotels and B&Bs," she said.