Mont. Code Ann. § 28-2-1712
28-2-1712 When stipulation against rescission ineffective
28-2-1712 . When stipulation against rescission ineffective. A stipulation that errors of description shall not avoid a contract or shall be the subject of compensation, or both, does not take away the right of rescission for fraud or for mistake where such mistake is in a matter essential to the inducement of the contract and is not capable of exact and entire compensation.