Hassan Beasley, a federal prisoner appearing pro se, appeals the district court’s denial of his motion for a sentence reduction pursuant to 18 U.S.C. § 3582(e)(2). Beasley pleaded guilty to a conspiracy to distribute crack cocaine and other drugs. He then faced a sentence guideline range of 151 to 188 months’ imprisonment based *827 on his status as a career offender under U.S.S.G. § 4B1.1. The district court sentenced him to 130 months in prison. Beasley contends that he now is eligible for a sentence reduction pursuant to Amendments 750 and 759 of the Sentencing Guidelines — which amended how quantities of drugs are calculated under U.S.S.G. § 2D1.1 — notwithstanding the fact that his guideline range was determined based on the career offender provision in U.S.S.G. § 4B1.1. Because these amendments did not alter Beasley’s sentencing range, we affirm the district court’s denial of his motion for a sentence reduction.

We review the district court’s legal conclusions regarding the scope of its authority under 18 U.S.C. § 3582(c)(2) de novo. United States v. James, 548 F.3d 983, 984 (11th Cir. 2008).

“As a general rule, district courts may not modify a term of imprisonment once it has been imposed, except in specific circumstances delineated in 18 U.S.C. § 3582(c).” United States v. Williams, 549 F.3d 1337, 1339 (11th Cir. 2008). Pursuant to § 3582(c)(2), the court is allowed to reduce a defendant’s prison term if the defendant was “sentenced to a term of imprisonment based on a sentencing range that has subsequently been lowered by the Sentencing Commission.” 18 U.S.C. § 3582(c)(2); see also U.S.S.G. § 1B1.10(a)(1). However, “[w]here a retroactively applicable guideline amendment reduces a defendant’s base offense level, but does not alter the sentencing range upon which his or her sentence was based, § 3582(c)(2) does not authorize a reduction in sentence.” United States v. Moore, 541 F.3d 1323, 1330 (11th Cir. 2008); see also U.S.S.G. § 1B1.10(a)(2)(B) (providing that a § 3582(c)(2) reduction is not authorized if the amendment “does not have the effect of lowering the defendant’s applicable guideline range”).

Amendment 750 to the Sentencing Guidelines lowered some of the drug-quantity calculations used under U.S.S.G. § 2D1.1. But, Beasley’s sentencing range was calculated under the career-offender guideline in U.S.S.G. § 4B1.1. 1 Accordingly, Amendment 750 did not alter the sentencing range upon which his sentence was based, and § 3582(c)(2) does not authorize a reduction in sentence. See Moore, 541 F.3d at 1330.

For these reasons, the district court did not err in denying Beasley’s § 3582(c)(2) motion, and we affirm.

AFFIRMED.