Tong Thanh Robert Nguyen pleaded guilty to conspiring to distribute and possess with intent to distribute 50 grams or more of cocaine base, in violation of 21 U.S.C. § 846, and the district court * sentenced him to 135 months in prison and 5 years of supervised release. On appeal, Nguyen argues the district court should have departed downward under U.S.S.G. § 4A1.3 because the seriousness of his criminal history was overstated, and he should be resentenced under United States v. Booker, — U.S.-, 125 S.Ct. 738, 160 L.Ed.2d 621 (2005), because the district court treated the Guidelines as mandatory at his pre-Booker sentencing.

As to the first issue, Nguyen cannot challenge his 135-month prison sentence because he specifically agreed to it in his plea agreement. See United States v. Reyes-Contreras, 349 F.3d 524, 525 (8th Cir. 2003) (per curiam); United States v. Nguyen, 46 F.3d 781, 783 (8th Cir. 1995). As to the second issue, Nguyen did not raise a Sixth Amendment objection below, and he cannot demonstrate a reasonable probability the district court would have imposed a lower sentence under advisory Guidelines. See United States v. Pirani, 406 F.3d 543, 552-53 (8th Cir. 2005) (en banc), petition for cert. filed, — U.S.L.W. - (U.S. July 27, 2005) (No. 05-5547).

Accordingly, we affirm the judgment of the district court.