IMAGE_ROOTFS_MAXSIZE, Hard Limit or safe to increase?

Bouncing against rootfs size limit when building with python pip.

ERROR: resin-image-1.0-r0 do_image_docker: The rootfs size 335872(K) overrides IMAGE_ROOTFS_MAXSIZE: 319488(K)

Is this a limit that can be safely extended, or was there a requirement indicating we should not go above the IMAGE_ROOTFS_MAXSIZE: 319488(K) limit?