To those who find it seriously difficult, because of their advanced age or for reasons peculiar to them, to observe the revised Liturgy of the Hours Pope Paul VI gave permission to keep using the previous Roman Breviary either in whole or in part. In 2007 Pope Benedict XVI allowed all clergy of the Latin Church to fulfil their canonical obligations by using the 1961 "Roman Breviary" issued under Pope John XXIII (but not earlier editions such as that of Pius X or Pius V). This is done by traditionalist Catholic communities, such as the Priestly Fraternity of St. Peter and the Institute of Christ the King Sovereign Priest.