A federal judge on Tuesday agreed to delay sentencing for Michael Flynn, President Donald Trump’s former national security adviser who has admitted to lying to the FBI.

Flynn, a Trump campaign supporter who stepped down from his adviser position in February 2017, will not be sentenced until March 13, U.S. District Judge Emmet G. Sullivan said. The extension was granted so that Flynn may finish cooperating with special counsel Robert Mueller’s team as it continues investigating possible collusion between the Trump campaign and Russian operatives.

Flynn reached a plea deal with Mueller’s team last December. Under the terms of the plea, he agreed to cooperate with the investigation and admit to lying to FBI agents.

Ahead of his announcement about the delay, Sullivan made it clear that prison time was a possibility for Flynn despite suggestions to the contrary from Mueller’s team.

“This crime is very serious,” Sullivan said.

“Arguably, you sold your country out,” he told Flynn.