Williams made the gaffe about Pulitzer Prize winner Eugene Robinson of The Washington Post on Monday.
After Robinson gave his commentary on President Barack Obama’s speech with Cuban President Raúl Castro, Williams tried to thank him. But instead of calling Robinson a columnist, the word “communist” slipped out.
Williams immediately corrected himself, saying, “You are not, in fact, a communist.”
Cuba’s communist government has been in power for more than 50 years.
Watch the moment above.
CORRECTION: A previous version of this story stated incorrectly that Robinson was a former employee of The Washington Post.