The U.S. Supreme Court ruled that rental-car drivers may have the right to prevent police from searching the vehicle, even if they aren’t authorized to drive it.

The court unanimously breathed new life into Terrence Byrd’s appeal of his conviction stemming from the heroin and illegal body armor that Pennsylvania state troopers found in the trunk of a car he was driving. Byrd’s girlfriend had rented the Ford Fusion, and he wasn’t on the rental agreement.

The high court said Byrd might have had a legitimate expectation of privacy within the car, reinstating his claim that police violated his constitutional right against unreasonable searches. The justices largely rejected arguments from the Trump administration, which was defending the federal court conviction.

"There may be countless innocuous reason why an unauthorized driver might get behind the wheel of a rental car and drive it -- perhaps the renter is drowsy or inebriated and the two think it safer for the friend to drive them to their destination," Justice Anthony Kennedy wrote for the court.

While that might violate the rental agreement, "the government fails to explain what bearing this breach of contract, standing alone, has on expectations of privacy in the car," Kennedy wrote.

The justices sent the case back to a federal appeals court to consider other arguments pressed by the Justice Department, including the claim that Byrd engaged in a "subterfuge" by having his girlfriend rent a car he was intending to drive.

Police pulled Byrd over on Interstate 81 outside Harrisonburg on the grounds that he hadn’t moved quickly enough into the right lane after passing a slow-moving truck.

Officers later learned that Byrd wasn’t on the rental agreement and had a criminal record as well as an arrest warrant in New Jersey. They told Byrd that, because he wasn’t an authorized driver, they didn’t need his consent to search the car.

Byrd pleaded guilty and was sentenced to 10 years in prison, but reserved his right to appeal. The Supreme Court ruling sets aside a federal appeals court decision that had upheld the conviction.

The case is Byrd v. United States, 16-1371.