How can post GRN with quantity exceeding of PO quantity

Hello experts,

I privation to sermon a scenario, if we created a PO for 100 quantity and the goods receipt is for 120. The GRN restricts that it cannot transcend 100. What is the imaginable solution truthful that we tin post  120 quantity and besides not person to edit the PO and however tin we way this successful the aboriginal that against this PO determination was a GRN of 120 quantity. And evidently determination volition beryllium an mistake connected the invoice erstwhile posting. Please suggest a solution for this scenario.