Hunter pleaded guilty under an agreement containing an appellate waiver and later challenged his sentence. The court of appeals enforced the waiver under circuit precedent allowing few exceptions. The Supreme Court held that an appellate waiver is not enforceable when enforcement would produce a miscarriage of justice, including an egregious legal error that would bring the judicial system into disrepute. The Court also clarified that a district court’s routine comments at the plea hearing do not automatically rewrite an otherwise valid written waiver. Because the lower court had not applied the proper miscarriage-of-justice inquiry, the judgment was vacated and the case remanded.