COOK, Circuit Judge. A jury convicted Charles Highgate of drug- and firearm-possession charges, and the district court sentenced him to an aggregate prison term of 360 months. Highgate appeals his conviction, arguing that a defense witness who invoked his Fifth Amendment privilege was improperly dismissed because the court did not inquire into the witness’s reasonable fear of prosecution. While we agree that the district court erred in accepting the witness’s blanket assertion without further probing, we affirm Highgate’s conviction because we find any resulting error harmless. Highgate also appeals his sentence, arguing that the court improperly treated the Sentencing Guidelines as mandatory and inadequately explained its analysis of the 18 U.S.C. § 3353(a) factors. Because the district court’s equivocation at sentencing does not assure us that it appreciated its full sentencing discretion, we vacate Highgate’s sentence and remand for resentencing consistent with this opinion.