Cameron Douglas admitted Thursday that he managed to get drugs in prison while serving a five-year sentence for an earlier drug plea.
Douglas entered the plea to a narcotics possession charge. He's agreed to serve another year in prison.
Douglas admitted possessing drugs from May through last week. That's when authorities found what appeared to be heroin and cocaine in his cell.
Federal Judge Richard Berman questioned whether security lapses at two federal prison facilities made it possible for Douglas to obtain drugs.
The 32-year-old son of the Academy Award-winning actor had previously admitted to dealing methamphetamine and cocaine.
He recently testified for the government in a drug trial as part of a cooperation deal.
