Prohibited Marriages -- Contracts

Mont. Code Ann. § 40-1-401, under Validity of Marriages -- Declaration of Invalidity.

Mont. Code Ann. § 40-1-401

(1) The following marriages are prohibited: (a) a marriage entered into prior to the dissolution of an earlier marriage of one of the parties; (b) a marriage between an ancestor and a descendant or between a brother and a sister, whether the relationship is by the half or the whole blood, or between first cousins; (c) a marriage between an uncle and a niece or between an aunt and a nephew, whether the relationship is by the half or the whole blood; (d) a marriage between persons of the same sex, as defined in 1-1-209. (2) Parties to a marriage prohibited under this section who cohabit after removal of the impediment are lawfully married as of the date of the removal of the impediment. (3) Children born of a prohibited marriage are legitimate. (4) A contractual relationship entered into for the purpose of achieving a civil relationship that is prohibited under subsection (1) is void as against public policy.