(1) 'Alteration' means:\n(a) An unauthorized change in an instrument that purports to modify in any respect the obligation of a party; or\n(b) An unauthorized addition of words or numbers or other change to an incomplete instrument relating to the obligation of a party.\n(2) Except as provided in subsection (3) of this section, an alteration fraudulently made discharges a party whose obligation is affected by the alteration unless that party assents or is precluded from asserting the alteration. No other alteration discharges a party, and the instrument may be enforced according to its original terms.\n(3) A payor bank or drawee paying a fraudulently altered instrument or a person taking it for value or for collection, in good faith and without notice of the alteration, may enforce rights with respect to the instrument:\n(a) According to its original terms; or\n(b) In the case of an incomplete instrument altered by unauthorized completion, according to its terms as completed. [1993 c.545 §48]
Oregon Legal Code