Gilberto Delgado-Ramirez appeals his sentence following his guilty-plea conviction of illegal reentry, in violation of 8 U.S.C. § 1326(a) and (b)(2). The district court sentenced him to 27 months of imprisonment, three years of supervised release, and a $100 special assessment.

Delgado-Ramirez argues that 8 U.S.C. § 1326(b)(2) is unconstitutional under Apprendi v. New Jersey, 530 U.S. 466, 120 S.Ct. 2348, 147 L.Ed.2d 435 (2000), be *748 cause it does not require the fact of a prior aggravated-felony conviction to be charged in the indictment and proved beyond a reasonable doubt. As Delgado-Ramirez concedes, this argument is foreclosed by Almendarez-Torres v. United States, 523 U.S. 224, 118 S.Ct. 1219, 140 L.Ed.2d 350 (1998), and Almendarez-Torres was not overruled by Apprendi. See United States v. Sarmiento-Funes, 374 F.3d 336, 346 (5th Cir. 2004).

For the first time on appeal, Delgado-Ramirez argues that, under United States v. Booker, — U.S. -, 125 S.Ct. 738, 160 L.Ed.2d 621 (2005), this court must vacate his sentence and remand for resentencing because the mandatory guideline regime was in place at the time of his sentencing. An unpreserved challenge to the computation of a defendant’s sentence under the formerly mandatory sentencing guidelines is reviewed for plain error. United States v. Mares, 402 F.3d 511, 520-21 (5th Cir. 2005), petition for cert. filed (Mar. 31, 2005) (No. 04-9517).

The district court’s application of the guidelines in their mandatory form constituted error that is “plain” for purposes of satisfying the first two prongs of the plain error analysis. See United States v. Valenzuela-Quevedo, 407 F.3d 728, 733 (5th Cir. 2005). Delgado-Ramirez must nevertheless show that the court’s error affected his substantial rights. Id. To make such a showing, Delgado-Ramirez bears the burden of demonstrating “that the sentencing judge — sentencing under an advisory scheme rather than a mandatory one— would have reached a significantly different result.” See Mares, 402 F.3d at 521. Delgado-Ramirez has failed to make such a showing. Accordingly, the judgment of the district court is AFFIRMED.