How to fix "error: symbol `grub_disk_get_size' not found."?

My computer was running a dual boot with Arch and Manjaro on their own partitions. I decided I wanted to exchange Manjaro for Debian, so I flashed the USB and deleted the Manjaro partition. Apparently that's the one Grub wants to boot from though, so I get shifted into grub rescue> mode. I want to at least boot into Arch, and ideally get a grub menu where I can boot from the USB containing the Debian installer. The problem is when I run insmod normal, I get the error in the title.