Back to The Future star Michael J. Fox has revealed that his Parkinson’s disease has begun affecting his short-term memory, leaving him unable to memorize lines for his latest roles.

The actor has been battling his disease publicly for that last two decades, which inspired his launching of the Michael J. Fox Foundation, a research center dedicated to finding a cure. While Fox has lived with the condition, he told People, “My short-term memory is shot.” He later bemoaned, “I always had a real proficiency for lines and memorization. And I had some extreme situations where the last couple of jobs I did were actually really word-heavy parts. I struggled during both of them.”

Fox revealed that instead of allowing this recent development to make him a defeatist, he remains positive by focusing his creativity in his writing. “I’m down to this,” he said of writing. “My guitar playing is no good. My sketching is no good anymore, my dancing never was good, and acting is getting tougher to do. So it’s down to writing. Luckily, I really enjoy it.”