As the error was performed by the god Indra, he grants Hanuman a want that his physique can be as potent as Indra's Vajra, Which his Vajra also can not harm him. Along with Indra other gods have also granted him wishes: the God Agni granted Hanuman a desire that https://www.reddit.com/user/HanumanJiMandir/comments/1avjbag/spiritual_experience_puja_at_hanuman_mandir/