The Arizona Supreme Court ruled Tuesday that drivers who have a non-impairing substance in their systems after smoking marijuana can’t be charged with driving under the influence. 

The case arose after a driver was pulled over and given a field sobriety test. After taking it, the driver admitted he had smoked pot the night before, and officers gave him a blood test. That test revealed a certain metabolite in his blood, and the state charged him with driving under the influence.

But in its ruling, the state’s high court said, “Drivers cannot be convicted of the offense based merely on the presence of a non-impairing metabolite that may reflect prior usage of marijuana.”

In a statement, Maricopa County Attorney Bill Montgomery, an opponent of the state’s medical marijuana law, says the court created ambiguity where it did not exist, and engaged in “interpretive jujitsu.”