An obligatory legal form for the validity of marriage was required by the Church for the first time by the Tametsi decree of the Council of Trent in 1563. The Ne temere decree (1907) and the Code of Canon Law (1917) confirmed this. For Eastern Catholic Christians the form was introduced in 1949 with Motu proprio Crebrae allatae. The form additionally applied to those who had abandoned the Catholic Church through a formal act. After the Second Vatican Council, however, an exception for them was incorporated into the Code of 1983. This exception was not found in CCEO (1990), as it was incompatible with the Eastern tradition. Adjustments to the CIC 1983, however, brought problems as to determining when and whether the “formal defection from the Catholic Church” occured with appropriate legal consequences. In order to remove those difficulties, the Holy Father Benedict XVI issued Motu proprio Omnium in mentem in Oct. 26, 2010, in which he abolished this exemption from the obligation of canonical form, the nullity of marriage with a non-christened and the prohibition of marriage with a non-catholic, to those, who has defected from the Catholic Church through a formal act.