Mont. Code Ann. § 28-2-206

A nonnegotiable written contract for the payment of money or the delivery of personal property may be transferred by endorsement the same as a negotiable instrument. The endorsement transfers all the rights of the assignor under the contract to the assignee, subject to all equities and defenses existing in favor of the maker at the time of the endorsement or arising before notice of the assignment is received by the maker.