The Supreme Court ruled Monday that police can use evidence seized during a traffic stop even if it turns out the officers were mistaken in thinking the driver had broken the law when they pulled the vehicle over.

The 8-1 decision written by Chief Justice John Roberts said that such a stop does not violate the Constitution's protection against unreasonable searches.

The ruling came in a North Carolina case in which a police officer pulled over Nicholas Heien's car because the right brake light was out, although the left one still worked. A search led to the discovery of cocaine in the trunk.

A state appeals court said the stop was impermissible because state law only requires a car to have one functioning brake light. But the state's highest court reversed, saying that the officer's misunderstanding of law was reasonable.

The Supreme Court agreed, finding that the Fourth Amendment requires police to act reasonably, but not perfectly. Roberts said that just as a police officer's mistake of fact can justify a traffic stop, a reasonable misunderstanding about the law can also satisfy the Constitution.

Heien had argued that ignorance of the law is no excuse for citizens accused of crimes and said there shouldn't be a double standard for police. But Roberts said that simply means the state can't impose a punishment for something that isn't illegal.