When is a defendant's agreement not to appeal their sentence unenforceable? Specifically, does the enforceability of an appeal waiver depend on whether its enforcement would result in a miscarriage of justice? Additionally, does a trial court's misstatement regarding appeal rights or a prosecutor's silence during sentencing void such a waiver?

• An appeal waiver is unenforceable when the disputed aspect of a sentence "violates a fundamental constitutional right."
• The District Court's representation at sentencing that the petitioner had a right to appeal, combined with the prosecutor's failure to object, voided the appeal waiver.
• The mandatory-medication condition of supervised release infringes on a "fundamental due process liberty interest in being free of unwanted mental health medication."

• Knowing and voluntary appeal waivers are always enforceable regardless of whether the sentence is unconstitutional.
• The Government did not waive or forfeit its right to enforce the waiver by failing to correct the District Court's misstatement at sentencing.
• A sentencing court may demand that a defendant take medication under 18 U.S.C. § 3563(b)(9) when the defendant has suffered from mental-health problems.

• An agreement not to appeal a sentence is unenforceable when it would result in a "miscarriage of justice," meaning it would leave in place an egregious error that would bring the judicial system into disrepute.
• The Court rejects the Government's position that knowing and voluntary waivers are always enforceable and the Fifth Circuit's rule limiting exceptions to ineffective assistance of counsel or sentences exceeding the statutory maximum.
• The reasoning is based on the judiciary's "independent" "institutional interest" in ensuring legal proceedings "appear fair to all who observe them," citing *Wheat v. United States* and *United States v. Mezzanatto*.
• Because courts are responsible for approving and implementing waivers, automatic enforcement of egregious errors risks "institutional harm."
• To qualify as a miscarriage of justice, the error must be obvious—not one a judge could reasonably make—and must be of the type that would undermine public confidence in the judiciary.
• Examples of such errors include sentences exceeding what the relevant statute allows; blatant constitutional errors (such as considering race or imposing an infirm condition of supervised release); and sentences imposed without "some minimum of civilized procedure."
• The Court held that the District Court's misstatement at sentencing did not modify the plea agreement because modifications must be in writing and signed by all parties, and there was no mutual consent (*Hawkins v. United States*).
• The Government did not waive or forfeit its right to enforce the waiver through silence, as the proper time to assert that right is after a notice of appeal is filed, citing *United States v. Olano*, *Garza v. Idaho*, and *Class v. United States*.