Nyle DiMarco expressed his thoughts about Jamie Foxx’s use of pretend “sign language” on Twitter.

Foxx was a guest at Jimmy Fallon‘s show on Friday, May 26. He made random gestures with his hands before Fallon transitioned to a commercial break.

The Dancing With the Stars season 22 winner, who is deaf, wrote on Twitter:  “It is straight up disrespectful to make up sign language. Everything is in gibberish.”

“How was this allowed?”, he continued. “Not comedy when you make fun of others.”

DiMarco later shared an open letter addressed to the actor. “Jamie Foxx’s behavior with Jimmy Fallon on Fallon Tonight should not be tolerated anymore,” he wrote. “We simply do not make fun at the expense of other cultures, especially those with a history of being marginalized. When we do this, progress takes a step backward.”

DiMarco concluded his letter by telling fans that his Nyle DiMarco Foundation is “working with other organizations to ensure every deaf child has a usable language before the age of 5,” adding, “What Foxx did on Fallon Tonight made our struggle that much harder.”