As the mistake was carried out because of the god Indra, he grants Hanuman a desire that his overall body can be as strong as Indra's Vajra, Which his Vajra might also not damage him. Coupled with Indra other gods have also granted him wishes: the God Agni granted Hanuman https://share.evernote.com/note/d4fdfcaa-2bec-7875-52f4-0feb94c33c95