diff --git a/docs/plat/qemu.rst b/docs/plat/qemu.rst
index 4ebe64b..a4c5bec 100644
--- a/docs/plat/qemu.rst
+++ b/docs/plat/qemu.rst
@@ -10,6 +10,10 @@
 BL2 edits the Flattened Device Tree, FDT, generated by QEMU at run-time to
 add a node describing PSCI and also enable methods for the CPUs.
 
+If ``ARM_LINUX_KERNEL_AS_BL33`` is set to 1 then this FDT will be passed to BL33
+via register x0, as expected by a Linux kernel. This allows a Linux kernel image
+to be booted directly as BL33 rather than using a bootloader.
+
 An ARM64 defconfig v4.5 Linux kernel is known to boot, FDT doesn't need to be
 provided as it's generated by QEMU.