Chidi Nwankwo appeals his judgment of conviction and sentence. The parties have expressly waived oral argument pursuant to Rule 34(j)(3), Rules of the Sixth Circuit, and we agree that oral argument is not necessary. Fed. R.App. P. 34(a).
Nwankwo pleaded guilty to a charge of possession of drugs with the intent to distribute them, a violation of 21 U.S.C. § 841(a)(1), (b)(1)(B). He was sentenced to 57 months of imprisonment to be followed by four years of supervised release.
In his timely appeal, Nwankwo argues that the sentencing judge erred by refusing to grant him downward departures from his calculated offense level based on his: (1) status as a deportable alien, (2) prospective prosecution for other crimes, (3) minimal or minor role in the offense, (4) extraordinary family circumstances, and (5) post-offense rehabilitation.
A district court’s refusal to depart downward is generally not reviewable. United States v. Pickett, 941 F.2d 411, 417-18 (6th Cir.1991). An exception exists, however, when the court’s refusal to depart is based upon a mistaken belief that it lacked authority to depart. Koon v. United States, 518 U.S. 81, 98-100, 116 S.Ct. 2035, 135 L.Ed.2d 392 (1996); United States v. Coleman, 188 F.3d 354, 357 (6th Cir.1999) (en banc). The sentencing judge stated that he assumed that he had the authority to grant a downward departure based on each of Nwankwo’s claims, yet he concluded that no departure was warranted on these grounds.
Because the district court did not reject Nwankwo’s grounds for departure based on a mistaken belief that it lacked the authority to do so, we will not review the *403issue further. See United States v. Owusu, 199 F.3d 329, 350 (6th Cir.2000).
Accordingly, we affirm the district court’s judgment.