As the error was done from the god Indra, he grants Hanuman a wish that his overall body can be as robust as Indra's Vajra, and that his Vajra can also not damage him. As well as Indra other gods have also granted him needs: the God Agni granted Hanuman https://www.evernote.com/shard/s419/sh/c3848c71-6862-0838-6da4-9fba5f7f1e8a/f0zpCEML9urmdze8mvX-WS6Mhch2pSuVEke_pL3lUOtjzhfCjyOo1Yi0Jw