When 8 December falls on Sunday the feast of the Immaculate Conception is celebrated on 9 December , save for in those places in which the Tridentine Mass and Office are still celebrated , in which case the feast is still celebrated on 8 December , with the Sunday Mass and Office being merely commemorated.
If December 8 is a Sunday , the Feast of the Immaculate Conception is celebrated the next day , except if the Tridentine Mass and Ofice are also celebrated on that day .