But it had nothing to do with performing on the show or winning three Moonmen.
While appearing on Wednesday's Chelsea Lately along with Ryan Lewis, the 30-year-old artist admitted his fear had more to do with his ladylove.
"I was scared about not thanking my fiancée," Macklemore told host Chelsea Handler. "And I did. Very last minute. I had already passed the mic to Ryan and then I remembered looking at her in the audience, and I was like, give that back, do not cue the music."
But despite having a fiancée, Macklemore nevertheless playfully acknowledged the persistent gay rumors.
"If you type in Macklemore...and you type 'is,' 'gay' pops up after 'is,' so, yes, the Internet thinks that I'm gay," he said. "It's not true."
Be sure to tune in to Chelsea Lately weeknights at 11 p.m. on E!