Friday April 26 07:22 PM EDT

An 18-year-old high school student who tested positive for nicotine during a random drug test will get to attend his prom after all.

Blackford High School had planned to ban Rob Mahon from its May 4 prom, saying he knew the school's rules prohibiting drugs, alcohol and nicotine before he agreed to taking the test, which is required for students in extracurricular activities.

But BHS's school district reversed the decision Friday after the Indiana Civil Liberties Union announced it would fight for Mahon (pictured, left) in court if necessary.

Mahon, who smokes cigarettes, said he didn't smoke on school property, and was upset that he was being punished for an activity that is legal for someone his age.