[Q] How do I properly use a prebuilt kernel with AOSP?

I'm trying to build AOSP for Moto X 2013 (ghost). I've successfully built the kernel separately already (and flashed it to my device to make sure it works) but I can't seem to find a way to tell AOSP to use it. I get the following error when running make -j16 otapackage:
No private recovery resources for TARGET_DEVICE ghost
make: *** No rule to make target `out/target/product/ghost/kernel', needed by `out/target/product/ghost/boot.img'. Stop.

I've already tried to add this line to device.mk:
LOCAL_KERNEL := device/motorola/ghost-kernel/zImage
But it did nothing.

Any ideas?