Sacerdotalis Caelibatus §42

⁴² In virtue of the fundamental norm of the government of the Catholic Church, to which We alluded above, (82) while on the one hand, the law requiring a freely chosen and perpetual celibacy of those who are admitted to Holy Orders remains unchanged, on the other hand, a study may be allowed of the particular circumstances of married sacred ministers of Churches or other Christian communities separated from the Catholic communion, and of the possibility of admitting to priestly functions those who desire to adhere to the fullness of this communion and to continue to exercise the sacred ministry. The circumstances must be such, however, as not to prejudice the existing discipline regarding celibacy. And that the authority of the Church does not hesitate to exercise her power in this matter can be seen from the recent Ecumenical Council, which foresaw the possibility of conferring the holy diaconate on men of mature age who are already married. (83)