John Gill Commentary Deuteronomy 27:22

"Cursed be he that lieth with his sister, the daughter of his father, or the daughter of his mother. And all the people shall say, Amen." — Deuteronomy 27:22 (ASV)

Cursed [be] he that lies with his sister Which is forbidden, (Leviticus 18:9); the daughter of his father, or the daughter of his mother; whether his sister by father or mother's side: and all the people shall say Amen; detesting such uncleanness.