Pope Francis has extended a new olive branch to a breakaway group of Catholic ultra-traditionalists, the Society of St Pius X, by allowing their priests to celebrate marriages.
The move follows his recent move to let priests in the Society hear confessions.
The conditions attached to the wedding authorisation were outlined in a letter to the Society approved by Francis and published by the Vatican on Tuesday.
They include having an officially recognised priest in attendance at the wedding or, if that is not possible, the Society priest must have express authorisation from the local bishop.
The letter said the latest step was part of "efforts to bring the Society of St. Pius X into full communion" and had been taken "despite the canonical irregularity in which for the time being (it) finds itself."
The Society was established in 1970 as a Church-approved group of clerics opposed to a package of liberalising Church reforms known as Vatican II.
In 1988, just under three years before his death, the group's leader Archbishop Marcel Lefebvre ordained a number of like-minded priests as bishops with the intention they could continue his battle.
He did so without the pope's permission and he and the new bishops were automatically excommunicated as a result.
The surviving Lefebvre loyalist bishops were allowed back into the Church in 2009, including Richard Williamson, a notorious British holocaust-denier.
Williamson was subsequently expelled from the Society and excommunicated for a second time last year after illicitly ordaining another bishop in Brazil.