The U.S. Supreme Court on Monday unanimously ruled a heroin dealer cannot be held liable for a client’s death and given a longer sentence if heroin only contributed to the death, and was not necessarily the only cause.

The ruling is likely to result in a shorter sentence for Marcus Burrage, who received 20 extra years in prison because of his client’s death, according to USA Today. The decision is also likely to make it more difficult in the future for prosecutors to extend drug sentences, the article notes.

A 1986 federal drug law requires a 20-year mandatory minimum sentence when “death or serious bodily injury results from the use” of drugs from a dealer. Burrage received a 20-year sentence for the drug sale, and an additional 20 years as a result of Joshua Banka’s death. According to an expert in the case, Banka’s death would have been “very less likely” if he had not used the heroin. However, Banka also had other drugs in his system, making it unclear whether heroin caused his death.

“Is it sufficient that use of a drug made the victim’s death 50 percent more likely? Fifteen percent? Five? Who knows?” Justice Antonin Scalia wrote in the ruling. “Uncertainty of that kind cannot be squared with the beyond-a-reasonable-doubt standard applicable in criminal trials or with the need to express criminal laws in terms ordinary persons can comprehend.”