As the error was performed because of the god Indra, he grants Hanuman a desire that his human body can be as sturdy as Indra's Vajra, and that his Vajra may also not hurt him. Coupled with Indra other gods have also granted him needs: the God Agni granted Hanuman https://shabarmantra49371.wssblogs.com/36900083/hanuman-for-dummies