fundamental-miscarriage-of-justice exception. The doctrine allowing a federal court in a habeas corpus proceeding to address a claim of constitutional error that, although ordinarily unreviewable, is subject to review because of a state-court procedural default that rendered the proceedings basically unfair. • For the exception to apply, among other things, the petitioner must show by a preponderance of the evidence that constitutional error resulted in the conviction of one who is actually innocent. If the defaulted claim applies only to sentencing, the exception permits review of the claim if the petitioner shows by clear and convincing evidence that, but for the constitutional error, no reasonable judge or jury would have imposed the sentence that the petitioner received. [Cases: Habeas Corpus 401.]