As the mistake was done because of the god Indra, he grants Hanuman a want that his system will be as strong as Indra's Vajra, Which his Vajra can also not harm him. Coupled with Indra other gods have also granted him wishes: the God Agni granted Hanuman a want https://israeltlaqf.bloggactif.com/38412345/details-fiction-and-hanuman