Pursuant to a plea agreement, Raymond Walker pled guilty to possession with intent to distribute marijuana, in violation of 21 U.S.C. § 841(a)(1), (b)(1)(D) (2000), and using and carrying a firearm during and in relation to, and possessing a firearm in furtherance of, a drug trafficking crime, in violation of 18 U.S.C.A. § 924(c)(1)(A) (West Supp. 2007). The district eoui-t sentenced Walker to ninety months in prison. Walker timely appealed.

Walker first contends that the district court exi'ed in accepting his guilty plea. Because Walker did not seek to withdraw his guilty plea in the distx’ict court and points to no eirors in the Fed.R.Crim.P. 11 heax'ing, we find that the district court did not plaixxly err in accepting his guilty plea. United States v. Martinez, 277 F.3d 517, 525 (4th Cir. 2002) (providing standard).

In addition, Walker argues that the district court erred by failing to downwax-dly depart from the guideline range pursuant to U.S. Sentencing Guidelines Manual § 5K2.13 (2005), based on his diminished capacity. A district court’s failure to grant a downward depax-ture is not reviewable unless the court was under the mistaken impression that it lacked the authoxity to depai't. United States v. Matthews, 209 F.3d 338, 352 (4th Cir. 2000); see also United States v. Cooper, 437 F.3d 324, 333 (3d Cir. 2006) (collecting cases declining to review district court’s decision not to depart, even after United States v. Booker, 543 U.S. 220, 125 S.Ct. 738, 160 L.Ed.2d 621 (2005)). Because Walker did not request a departure, the district court did not consider a departure based on his diminished capacity and thus did not make any decisions concerning its authoxity to depai't on that ground. We therefore lack jurisdiction to review the distinct court’s failure to depart sua sponte.

Accordingly, we affirm the judgment of the distinct coui’t. We dispense with oi'al ax'gument because the facts and legal contentions are adequately presented in the materials before the court and ax-gument would not aid the decisional process.

AFFIRMED.