Perhaps Britain's Prince Harry should move to Idaho.

In overturning an impaired driving conviction, the 9th U.S. Circuit Court of Appeals ruled Monday that a loophole in Idaho law means marijuana users can drive legally as long as they don't drive erratically and can pass a field sobriety test.

A three-judge panel of the San Francisco-based court wrote that Idaho's impaired driving law makes it illegal to drive under the influence of alcohol and narcotics. But Idaho doesn't list marijuana as a narcotic.

The court said that because marijuana is not listed as a narcotic, Matthew Patzer could not automatically be presumed impaired, like motorists who have been drinking alcohol.

In overturning the 21-year-old's conviction, the court wrote that he was pulled over for a broken tailgate light, wasn't driving erratically and passed a field sobriety test.

"Given the distinction drawn by the statute, there is no basis to conclude that impairment may be presumed upon admission of use of a non-narcotic drug," the appeals court wrote.

After a New Plymouth, Idaho, police officer noticed his glassy eyes, Patzer admitted to smoking marijuana at a party on Sept. 27, 1998. Patzer passed two field sobriety tests before being arrested for driving impaired.

Idaho Senate Judiciary Chairman Denton Darrington said he had assumed marijuana was a narcotic under state law, and that the statute might need to be reviewed. But he questioned whether Monday's decision would hold up on appeal.

"My guess is, in light of the record of the 9th Circuit with the U.S. Supreme Court ... that the government will take it on up," Darrington said. "We may have to evaluate our law, but first we'll see what the government does here."

Darrington was referring to the circuit's reputation of being overturned by the U.S. Supreme Court.

Patzer's attorney, Fredilyn Sison of the office of the Federal Defenders of Eastern Washington and Idaho, applauded the decision.

"Just having smoked marijuana doesn't give somebody cause to arrest you for that when driving," Sison said.

Assistant U.S. Attorney Michael J. Fica, in Pocatello, Idaho, said the government was considering asking the circuit to review its decision or requesting the U.S. Supreme Court to hear the case.

The circuit's decision also reverses Patzer's illegal weapons convictions. In his Chevrolet Blazer, police found four illegal homemade grenades, a sawed-off shotgun and a modified rifle with a homemade silencer.

The court said that because of his unlawful arrest, authorities illegally searched his vehicle. The decision reverses U.S. District Judge Edward J. Lodge.

"Patzer's arrest was unlawful. The evidence obtained after his arrest ... were 'fruit of the poisonous tree' and should have been suppressed by the district court," the three-judge panel wrote.

The case is United States v. Patzer.