X17

I have windows 10 and I'm trying to dual boot windows 7 along with it. I mounted the iso to my usb, and partitioned my drive. When I try to select any drive on the windows 7 installation screen it says "Windows cannot be installed to this disk. The selected disk is not of the GPT partition style". I can't figure out why it's doing this, could it be something wrong with the iso? I downloaded ultimate edition 64 bit from the August 2018 option.