The Indiana Supreme Court on Thursday overturned a man’s conviction for not registering as a sex offender because he had already completed a sentence for child molesting before the state’s Sex Offender Registration Act was enacted.

In a unanimous ruling, the court said the subsequent conviction of Richard P. Wallace two years ago violated the state constitution’s prohibition of retroactive laws.

Applying the sex registration requirement to Wallace, who completed his probation two years before the law was enacted, would impose “burdens that have the effect of adding punishment beyond that which could have been imposed when his crime was committed,” Justice Robert Rucker wrote in an 18-page opinion.

Wallace pleaded guilty to one count of child molesting in 1989 and was given a five-year suspended sentence plus probation. He completed the probation in 1992. In 1994, the legislature passed a law requiring registration of sex offenders. The law was amended in 2001 to require registration regardless of when the offenders were convicted, and Wallace’s ex-wife notified authorities in 2003 that he had never registered.