As the mistake was done by the god Indra, he grants Hanuman a want that his human body will be as strong as Indra's Vajra, and that his Vajra may also not harm him. In conjunction with Indra other gods have also granted him needs: the God Agni granted Hanuman https://www.evernote.com/shard/s426/sh/32d0246d-d1d3-b0d2-f3af-bd2b2e964610/3402CZr4J9QpvM3UxDNw4mDsTQA0SJ-lyVoicsr_n5jjJWrbJuc88h2hTA