Error correction

Hello. In the following exercise I'm supposed to spot the mistake:
"My brother has been getting so nervous with me recently - I've no idea what's the matter with him.
Apparently, the only mistake, according to the answer key is the word "nervous", which should be "irritable", but surely isn't "what's the matter with him" a mistake too? Being an indirect question, shouldn't it be "what the matter with him is"? Thank you very much.