An officer’s objectively reasonable mistake of law may provide the reasonable suspicion necessary to justify a traffic stop under the Fourth Amendment. An officer pulled Heien and his companion over for driving with one broken brake light. During the stop, Heien consented to a search of his vehicle. The officer found cocaine and Heien was charged with attempted trafficking. The trial court denied his motion to suppress, and he pled guilty. On appeal, he argued that the stop was not valid because North Carolina law only required one working brake light, which he had. The North Carolina Supreme Court ultimately concluded that, even assuming the faulty break light was not a violation, suppression was not required because the officer made a reasonable mistake of law. The U.S. Supreme Court granted certiorari. Held: Affirmed. The Fourth Amendment requires officers to have reasonable suspicion that a person is breaking the law before they may conduct a traffic stop. In this case, the Court concluded that the reasonable suspicion necessary for a traffic stop may be based on a reasonable mistake of law. Reasonable suspicion arises from a combination of an officer’s understanding of the facts and the law, and the officer may be reasonably mistaken on either ground. This conclusion is supported by United States v. Riddle (1809) 5 Cranch 311 and its progeny (which discuss mistakes of law in a related context) and Michigan v. DeFillippo (1979) 443 U.S. 31. An officer’s mistake of law must be objectively reasonable and his subjective understanding of the law is irrelevant. Additionally, mistakes about the requirements of the Fourth Amendment, even if reasonable, can never support a search or seizure. Here, the officer’s mistake was objectively reasonable because the statute at issue arguably indicated that, if a vehicle has multiple brake lights, all must be functional and the provision had not previously been construed by the appellate courts.