Learn English – Word to describe a person who tolerates other people’s mistakes

A close friend of mine is a tech support and I'd like to give him card and compliment on his tolerance for (sometimes silly) mistakes.

I'm looking for a word to describes a person that tolerates others' mistakes. For example, this person might be a school teacher who wouldn't be angry because a kid made a mistake or a boss in a company who wouldn't get mad because his or her employees messed up.

I'm looking for something other than tolerant because I would like to be specific and narrow down the scope to be just tolerant towards mistakes.

On the other hand, I feel words like nice, patient, and the like all entail some level of tolerance towards others' mistakes. Moreover, this quality of tolerance for mistakes doesn't necessarily entail that this person is nice or friendly. It may be because it's his job and he's a competent employee. I may be wrong and this's way too specific, but I wonder if there's a word depicts exactly that.

Either noun or adjective will work! I just want it to be one word so it looks good on the cover of the card!