The actor's role as the Trinity killer on the Showtime drama won him an Emmy for 'Outstanding Guest Actor In A Drama Series'.
However, in his speech, Lithgow accidentally thanked HBO, rather than Showtime, for his win.
"I'll never live that down. They'll probably be taking this back now," he joked in an interview with Access Hollywood.
He also credited his Emmy success to the show's writers, praising their creation of the Trinity character.
"The Trinity killer was such an amazing character they created and such a wonderful piece of suspenseful storytelling, it just kept people wanting to see the next week's episode," he said.
Lithgow recently hinted that he could reprise his role in the new season of Dexter.
The series returns to Showtime on September 26.