Ask for two different self-evaluations, an official one that can be used to give him a raise and an unofficial one that can be used for self-improvement. Make sure he doesn't confuse the two. In the future, try to intercept his official self-evaluation if possible, just to make sure he understood you. 

But don't try to deny his observations. They're probably correct. People who are at the top of their game are extremely critical of themselves. That's how they're able to improve their skills year after year.