In this opinion, we consider whether the United States Supreme Court decisions in Welch v. United States, 578 U.S. ----, 136 S.Ct. 1257, 194 L.Ed.2d 387 (2016), and Montgomery v. Louisiana , 577 U.S. ----, 136 S.Ct. 718, 193 L.Ed.2d 599 (2016), constitute good cause to overcome the procedural bars to a postconviction petition for a writ of habeas corpus in which the petitioner contends he is entitled to the retroactive application of a nonconstitutional substantive rule. Welch and Montgomery do not alter the threshold requirement that, for a new substantive rule to apply retroactively, it must be a constitutional rule. We hold the decisions in those cases do not constitute good cause to raise a procedurally barred claim arguing a nonconstitutional rule should be applied retroactively. Therefore, we conclude the district court did not err by finding Branham failed to demonstrate good cause or a fundamental miscarriage of justice to overcome the procedural bars to his petition. Accordingly, we affirm.

PROCEDURAL HISTORY

William Edward Branham was convicted in 1993 of first-degree murder. The Nevada Supreme Court affirmed Branham's conviction on direct appeal. See Branham v. State , Docket Nos. 24478 & 24648 (Order Dismissing Appeals, December 18, 1996). Thereafter, Branham filed a timely postconviction petition for a writ of habeas corpus, which was resolved on its merits, and a subsequent, procedurally barred petition. The district court orders resolving those petitions were affirmed on appeal. See Branham v. State, Docket No. 45532 (Order of Affirmance, November 10, 2005); Branham v. Warden, Docket Nos. 33830 & 33831 (Order Dismissing Appeals, February 15, 2000).

Branham filed the instant postconviction petition for a writ of habeas corpus on April 7, 2017, more than 20 years after the remittitur was issued from his direct appeal. He claimed he is entitled to the retroactive benefit of the narrowed definition of "willful, deliberate and premeditated" murder announced *315in Byford v . State, 116 Nev. 215, 236-37, 994 P.2d 700, 714-15 (2000), and, accordingly, his convictions should be set aside and he should receive a new trial wherein the jury is properly instructed. Although acknowledging his petition was subject to procedural bars, Branham asserted the recent United States Supreme Court decisions in Welch and Montgomery provided good cause to raise this claim. The district court dismissed Branham's petition as procedurally time-barred, finding he failed to demonstrate good cause or a fundamental miscarriage of justice to overcome the procedural bars. This appeal follows.

ANALYSIS

Branham claims the district court erred by dismissing his petition as procedurally barred. Branham acknowledges his petition was subject to procedural bars, see NRS 34.726(1) ; NRS 34.810(1)(b), (2), but he argues the district court erred by finding he failed to demonstrate good cause or a fundamental miscarriage of justice to overcome the procedural bars.1

The application of procedural bars is mandatory, see State v. Eighth Judicial Dist. Court (Riker), 121 Nev. 225, 231, 112 P.3d 1070, 1074 (2005), but a petitioner may overcome the bars in one of two ways: (1) by demonstrating good cause and actual prejudice, see NRS 34.726(1) ; NRS 34.810(3), or (2) by demonstrating actual innocence, such that a fundamental miscarriage of justice would result were the underlying claims not heard on the merits, see NRS 34.800(1)(b) ; Pellegrini v. State, 117 Nev. 860, 887, 34 P.3d 519, 537 (2001). As discussed below, we conclude the district court did not err by finding Branham failed to overcome the procedural bars.

Branham did not demonstrate good cause

To demonstrate good cause to overcome the procedural bars, a petitioner must offer a legal excuse by showing "that an impediment external to the defense prevented him ... from complying with the state procedural default rules." Hathaway v. State, 119 Nev. 248, 252, 71 P.3d 503, 506 (2003). That is, a petitioner must show "that the factual or legal basis for a claim was not reasonably available ... or that some interference by officials, made compliance impracticable." Id. (internal quotation marks omitted).

Branham claims he demonstrated good cause to overcome the procedural bars because the recent United States Supreme Court decisions in Welch and Montgomery expand the reach of federal retroactivity jurisprudence to state collateral proceedings.

In both Welch and Montgomery, the issue before the Court was whether an earlier decision announced a new, substantive rule of constitutional law that must be applied retroactively to cases that were final when the earlier decision was rendered. See Welch, 578 U.S. at ----, 136 S.Ct. at 1261 ; Montgomery, 577 U.S. at ----, 136 S.Ct. at 732-34. The question in Welch was whether the prior decision constituted a new substantive constitutional rule. 578 U.S. at ----, 136 S.Ct. at 1261. In deciding this question, the Court held that whether a rule is characterized as procedural or substantive depends on the function of the new rule, "not the constitutional guarantee from which the rule derives." Id. at ----, 136 S.Ct. at 1266. The question in Montgomery was whether "the Constitution requires state collateral review courts to give retroactive effect" to "a new substantive rule of constitutional law [that] controls the outcome of a case." 577 U.S. at ----, 136 S.Ct. at 729. The court held the answer was yes. Id.

Branham asserts these decisions establish that the substantive rule exception to the federal retroactivity framework requires states to apply any new substantive rule, including a decision narrowing the interpretation of a criminal statute, retroactively. In particular, Branham claims that Welch implies "the clarification/change in law dichotomy [in retroactivity analysis] has become essentially *316obsolete" and, after Welch, the only relevant question is whether the new interpretation represents a new substantive rule. Branham argues that the decision in Byford set forth a new substantive rule and, as a result, the decisions in Welch and Montgomery provide a legal basis that was not previously available to support his underlying claim that he is entitled to the retroactive application of Byford. Branham is mistaken as to the implications of the holdings of Welch and Montgomery.

The United States Supreme Court first set out its modern retroactivity framework in the plurality opinion Teague v. Lane, 489 U.S. 288, 109 S.Ct. 1060, 103 L.Ed.2d 334 (1989). Teague established that new constitutional rules, i.e., rules of criminal procedure that have an underlying constitutional source, generally do not apply retroactively to convictions that were final when the new constitutional rule was announced. Id. at 306-07, 109 S.Ct. 1060. However, Teague recognized two categories of constitutional rules that are not subject to its retroactivity bar. Montgomery, 577 U.S. at ----, 136 S.Ct. at 728. "First, courts must give retroactive effect to new substantive rules of constitutional law." Id. "Second, new watershed rules of criminal procedure, which are procedural rules implicating the fundamental fairness and accuracy of the criminal proceeding, will also have retroactive effect." Welch , 578 U.S. at ----, 136 S.Ct. at 1264 (internal quotation marks omitted). The threshold requirement for the applicability of Teague's retroactivity framework is that the new rule at issue must be a constitutional rule.2 See Teague , 489 U.S. at 306, 109 S.Ct. 1060.

In both Welch and Montgomery , the Court applied the existing Teague retroactivity framework to decide the issue before it. See Welch, 578 U.S. at ----, 136 S.Ct. at 1264-68 ; Montgomery, 577 U.S. at ----, 136 S.Ct. at 728-36. Nothing in either case alters Teague's threshold requirement that the new rule at issue must be a constitutional rule. See Welch, 578 U.S. at ----, 136 S.Ct. at 1264 (reiterating that the Teague retroactivity framework applies to new constitutional rules); Montgomery, 577 U.S. at ----, 136 S.Ct. at 728 (same). Because the decisions in Welch and Montgomery do not alter this threshold requirement, we hold those decisions do not constitute good cause for raising a procedurally barred claim arguing a nonconstitutional rule should be applied retroactively.

Here, Branham claimed the decisions in Welch and Montgomery provided good cause to raise his Byford claim. However, the decision in Byford "was a matter of interpreting a state statute, not a matter of constitutional law," and "[n]othing in the language of Byford suggests that decision was grounded in constitutional concerns." Nika, 124 Nev. at 1288, 198 P.3d at 850. Because the decision in Byford did not establish a new constitutional rule, the decisions in Welch and Montgomery do not constitute good cause for Branham to raise his procedurally barred claim that Byford must be applied retroactively.3

Branham did not demonstrate a fundamental miscarriage of justice

Branham also claims he demonstrated a fundamental miscarriage of justice to overcome the procedural bars. A district court may reach the merits of any claims of constitutional error where a petitioner can demonstrate a fundamental miscarriage of justice has resulted in the conviction of one who is actually innocent.

*317Pellegrini , 117 Nev. at 887, 34 P.3d at 537. Branham's argument fails for two reasons.

First, a successful claim of a fundamental miscarriage of justice only allows for consideration on the merits of claims of constitutional error. But because the Byford decision was not grounded in constitutional concerns, Branham's underlying Byford claim was not a claim of constitutional error. Accordingly, Branham would not have been entitled to have his underlying Byford claim decided on the merits. Second, Branham could not demonstrate he was actually innocent. See Mitchell v. State, 122 Nev. 1269, 1273-74, 149 P.3d 33, 36 (2006) (" '[A]ctual innocence' means factual innocence, not mere legal insufficiency." (alteration in original) (quoting Bousley v. United States, 523 U.S. 614, 623, 118 S.Ct. 1604, 140 L.Ed.2d 828 (1998) ) ). He thus failed to demonstrate dismissal of his claim would result in a fundamental miscarriage of justice.

CONCLUSION

We hold that the United States Supreme Court decisions in Welch and Montgomery do not constitute good cause to raise a procedurally barred claim arguing that a nonconstitutional rule should be applied retroactively. Because the decision in Byford did not establish a new constitutional rule, we conclude the district court did not err by finding the decisions in Welch and Montgomery did not constitute good cause for Branham to raise his procedurally barred claim that Byford must be applied retroactively.4 Branham also failed to demonstrate that dismissal of his claim would result in a fundamental miscarriage of justice. Accordingly, we affirm the district court's order dismissing Branham's postconviction petition for a writ of habeas corpus as procedurally barred.