MANKATO, Minn. (AP) — The state Court of Appeals has thrown out the conviction of a southern Minnesota man, saying the amount of meth-tainted water found in his bong was far under the threshold required for his imprisonment.

In 2013, 32-year-old Ryan Drown was sentenced to 6 1/2 years in prison for having the tainted water in a bong that amounted to less than half an ounce. But a 2011 amendment to a law required at least four ounces of water for such a serious conviction.

Drown was in prison for seven months and was granted release in July 2014 pending an appeal. The court ruling in his favor came last week.

Prosecutor Chris Rovney says trial lawyers and the judge made a mistake. State Representative Phyllis Kahn, chief sponsor of the bong water legislation, says it's surprising the change in the law wasn't caught in Drown's trial.