Appellant’s vehicle was stopped for a taillight infraction. When the officer approached appellant, he noticed that he appeared to have been smoking marijuana. The officer arrested appellant for driving under the influence after administering field sobriety tests, leading appellant to admit that he had been smoking marijuana, and obtaining his consent to search the vehicle. Weapons were found in the vehicle. The trial court denied appellant’s suppression motion, holding that the search was incident to the arrest for driving under the influence. The Ninth Circuit here reversed. The applicable Idaho driving under the influence statute provides that it is unlawful for a person to drive under the influence of alcohol or a narcotic drug. Idaho law also does not define marijuana as a narcotic drug. Therefore, the officer did not have probable cause to believe appellant was driving under the influence of a narcotic. An officer may not arrest a person for driving under the influence of a non-narcotic drug without probable cause to believe the person’s ability to drive safely is impaired. Here, the officer had no probable cause to believe that appellant’s driving ability was impaired. Therefore, the arrest was unlawful, and the evidence should have been suppressed.