(CNN) Deputy Attorney General Rod Rosenstein still has his day job as the No. 2 official at the Justice Department, but he will make a guest appearance at the Supreme Court later this month, according to a source familiar with the matter.

Rosenstein will argue a case on behalf of the United States in a technical matter concerning sentencing guidelines on April 23.

A source close to Rosenstein tells CNN he is expected to appear in formal morning clothes for the occasion. He borrowed the jacket from the Solicitor General's office, the source said.

There is precedent for this type of rare appearance from a top official outside of the Solicitor General's office. In 2008, then-Attorney General Michael Mukasey argued in a terrorism case.

In the case Rosenstein is handling, the justices are being asked to resolve a circuit split concerning how much explanation lower courts must provide when granting a motion to reduce a defendant's criminal sentence.

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