As the mistake was done because of the god Indra, he grants Hanuman a desire that his overall body might be as robust as Indra's Vajra, and that his Vajra also can not damage him. In addition to Indra other gods have also granted him wishes: the God Agni granted https://share.evernote.com/note/06258cba-9fed-2580-a0aa-eb4d9ff9e253