As the error was accomplished because of the god Indra, he grants Hanuman a desire that his system could well be as powerful as Indra's Vajra, and that his Vajra might also not damage him. Along with Indra other gods have also granted him wishes: the God Agni granted Hanuman https://sites.google.com/view/hindu-temple-south-australia/embracing-the-teachings-of-lord-shanidev-at-hanuman-mandir-adelaide