The U.S. Supreme Court on Thursday ruled against a pair of criminal defendants facing a 15-year mandatory minimum prison sentence in light of their previous drug convictions, holding that later changes to the federal drug schedule have no effect on sentencing enhancements for supposed armed career criminals.

In its 6-3 ruling in Brown v. United States, the court said judges should consider the seriousness of a prior drug conviction at the time of that conviction in determining whether to impose a steep sentencing enhancement on defendants later convicted as a felon in possession of a firearm.