
    UNITED STATES of America, Plaintiff-Appellee, v. Jorge MENDOZA-BLANCO, also known as Angelo Rodriguez-Carabel, Defendant-Appellant.
    No. 04-41499.
    United States Court of Appeals, Fifth Circuit.
    Feb. 14, 2006.
    
      Marjorie A. Meyers, Fed. Pub. Def., Timothy William Crooks, Asst. Fed. Pub. Def., Houston, TX, for Defendant-Appellant.
    Before HIGGINBOTHAM, BENAVIDES and DENNIS, Circuit Judges.
   PER CURIAM:

Jorge Mendoza-Bianco pleaded guilty to attempted illegal reentry following deportation in violation of 8 U.S.C. § 1326. The presentence report (“PSR”) recommend an offense level of 24, which included a 16-level increase for a prior conviction. Mendoza-Bianco objected to the PSR on the basis of Blakely v. Washington, which the district court denied in light of our decision in United States v. Pineiro. Mendoza-Bianco now appeals his 100-month sentence pursuant to United States v. Booker. Because Mendoza-Bianco preserved his claim of error and the government cannot show the error is harmless, we VACATE Mendoza-Blanco’s sentence and REMAND to the district court for resen-tencing.

Because the district court sentenced Mendoza-Bianco under a mandatory Guidelines regime, it committed Fanfan error. The government concedes that Mendoza-Blanco’s objection on the basis of Blakely was sufficient to preserve his Fan-fan claim. Our review of preserved Fan-fan claims is for harmless error. Because Fanfan error is a nonconstitutional error, the government must show that the error was harmless beyond a reasonable doubt.

Under harmless error, an error that does not affect a defendant’s “substantial rights” is disregarded. Thus, the government must prove that the outcome of the district court proceedings was not affected by the imposition of the mandatory Guidelines. Here, the government argues that no prejudice resulted to the defendant because the sentencing judge gave no indication that it wanted to impose a lesser sentence. We are not persuaded, particularly in light of the sentencing judge’s decision to impose' the minimum sentence under the Guidelines.

Accordingly, we VACATE Mendoza-Blanco’s sentence and REMAND for re-sentencing. 
      
      . 542 U.S. 296, 124 S.Ct. 2531, 159 L.Ed.2d 403 (2004).
     
      
      . 377 F.3d 464, 465-66 (5th Cir.2004).
     
      
      . 543 U.S. 220, 125 S.Ct. 738, 160 L.Ed.2d 621 (2005).
     
      
      . See United. States v. Valenzuela-Quevedo, 407 F.3d 728, 733 (5th Cir.2005).
     
      
      . See United States v. Mares, 402 F.3d 511, 520 n. 9 (5th Cir.2005) ("[I]f either the Sixth Amendment issue presented in Booker or the issue presented in Fanfan is preserved in the district court by an objection, we will ordinarily vacate and remand, unless we can say the error is harmless under Rule 52(a) of the Federal Rules of Criminal Procedure.”).
     
      
      . See Valenzuela-Quevedo, 407 F.3d at 732-34 (discussing the difference between Sixth Amendment Booker error and nonconstitu-tional Fanfan error).
     
      
      
        .United States v. Walters, 418 F.3d 461, 464 (5th Cir.2005). Although we must follow the panel's decision in Walters, United States v. Ruiz, 180 F.3d 675, 676 (5th Cir.1999), we note that the standard of review it applied— requiring the Government to show that preserved Fanfan error was harmless beyond a reasonable doubt — was not contested in the case and appears to be incorrect because Fan-fan error is nonconstitutional error. See United States v. Hughes, 401 F.3d 540, 553 (4th Cir.2005) (pointing out that Fanfan error, unlike Booker error, is nonconstitutional). Rather, "harmless error” in Fanfan cases is defined by the standard announced in Kotteakos v. United States, 328 U.S. 750, 776, 66 S.Ct. 1239, 90 L.Ed. 1557 (1946). See United States v. Hernandez-Guevara, 162 F.3d 863, 876 (5th Cir.1998) (applying Kotteakos’s "substantial and injurious effect” standard to preserved nonconstitutional error). But the issue is irrelevant here because the Government cannot meet either burden.
     
      
      . Fed. R.Crim. P. 52(a).
     
      
      . Cf. United States v. Rodnguez-Gutierrez, 428 F.3d 201, 205-06 (5th Cir.2005).
     
      
      . Mendoza presents two additional arguments on appeal. First, to preserve the issue for Supreme Court review, Mendoza challenges the constitutionality of § 1326, but he correctly concedes that this argument is foreclosed. See Almendarez-Torres v. United States, 523 U.S. 224, 235, 118 S.Ct. 1219, 140 L.Ed.2d 350 (1998); United States v. Alfaro, 408 F.3d 204, 210-11 (5th Cir.2005), cert. denied, 126 S.Ct. 271 (Oct. 3, 2005). Second, Mendoza argues that the government breached an oral plea agreement by failing to recommend a three-level sentence reduction for Mendoza-Blanco's acceptance of responsibility under U.S.S.G. § 3E1.1. Since we vacate and remand because of the sentencing judge’s Fanfan error, we need not address this issue.
     