I found a solution to this problem in the following thread:
In short, I had to do the following before running the nvidia driver installation program:
cp /boot/vmlinuz.config /usr/src/linux/.config
cp /boot/vmlinuz.version.h /usr/src/linux/include/linux
cp /boot/vmlinuz.autoconf.h /usr/src/linux/include/linux
make cloneconfig dep
I didn't think this was necessary, since I already had the kernel sources installed, but this worked for me.