The U.S. Supreme Court on Monday ruled that police officers don't necessarily violate a person's constitutional rights when they stop a car based on a mistaken understanding of the law. The ruling prompted a lone dissent from Justice Sonia Sotomayor, who warned that the court's decision could exacerbate public suspicion of police in some communities.

In 2009, Nicholas Heien and a friend were traveling down a North Carolina highway when they were pulled over for having a broken tail light. A subsequent search of the car found a plastic bag containing cocaine. It turns out, though, that police had no legal right to stop the car in the first place because, under North Carolina law, having a single broken tail light is not an offense. Heien contended that just as ordinary citizens cannot claim ignorance of the law as a defense, police can't either, and because the traffic stop was illegal, the evidence from the search that followed should not have been permitted in evidence against him.

But the Supreme Court, by an 8-1 vote, ruled that since the officer's mistake was reasonable, it did not violate the constitution's ban on unreasonable searches and seizures, NPR reports.

Writing for the court, Chief Justice John Roberts noted that the keystone of the Fourth Amendment ban on unreasonable search and seizure is the word "unreasonable." And in this case, the officer's belief that having a broken tail light was illegal counted as a reasonable mistake. The traffic stop and the subsequent consensual search of the car were therefore also reasonable.