Former President Donald Trump was met with boos Sunday after announcing to a mostly unmasked crowd he had, in fact, received a booster dose of the COVID-19 vaccine, Newsweek reports.

Appearing alongside former Fox host Bill O’Reilly at the American Airlines Center in Dallas during the final stop of their “History Tour,” Trump confirmed his booster status and even told those chiding him (and presumably O’Reilly, who also said he is boosted) to essentially knock it off.

The interaction between Trump and the crowd made for an “interesting moment,” notes New York Times reporter Maggie Haberman, considering “some around Trump are now mocking the booster campaign.”

The ex-president also told his supporters they should “take credit” for the vaccines, as they were developed during his administration. 

“Look, we did something that was historic, we saved tens of millions of lives worldwide when we, together, all of us, we got a vaccine done,” Trump said, per Newsweek. “This was going to ravage the country far beyond what it is right now, take credit for it … it’s great, what we’ve done is historic. Don’t let them take it away.”