diff --git a/doc/README.fdt-control b/doc/README.fdt-control
index e6d5ed0..29fd56a 100644
--- a/doc/README.fdt-control
+++ b/doc/README.fdt-control
@@ -156,7 +156,10 @@
 Be aware that this environment variable is checked prior to relocation,
 when only the compiled-in environment is available. Therefore it is not
 possible to define this variable in the saved SPI/NAND flash
-environment, for example (it will be ignored).
+environment, for example (it will be ignored). After relocation, this
+variable will be set to the address of the newly relocated fdt blob.
+It is read-only and cannot be changed. It can optionally be used to
+control the boot process of Linux with bootm/bootz commands.
 
 To use this, put something like this in your board header file: