[U-Boot] mkimage: path behavior for FIT images

I have following folder structure:

board/kernel_fdt.its output/images/zImage

The kernel.its has following path for the zImage:

data = /incbin/("output/images/zImage");

When I invoke mkimage like this, it complains, that "output/images/zImage" doesn't exist:

mkimage -f board/kernel_fdt.its output/images/kernel_fdt.itb

in other words it seems to take zImage's relative path starting from "board", where kernel_fdt.its is located. Is it a desired behavior and how can I override it, so that root will be set to the mkimage invocation path?

Regards, Yegor