Or. Rev. Stat. § 254.399 – When ballot considered legally cast; when vote counted; prohibition on voting more than once in same election

(1) A ballot shall be considered legally cast if the person casting the ballot is an elector at the time the ballot is cast.
(2) A vote for a particular candidate or on a measure shall be counted if the elector is qualified to vote for the particular candidate or on the measure.
(3) If an elector has voted in any election, the elector may not register or update a registration and vote in any election held on the same date. [Formerly 247.007]