As the mistake was completed from the god Indra, he grants Hanuman a wish that his overall body might be as sturdy as Indra's Vajra, and that his Vajra can also not hurt him. In conjunction with Indra other gods have also granted him wishes: the God Agni granted Hanuman https://directoryethics.com/listings13320064/not-known-factual-statements-about-hanuman