diff --git a/sys/boot/i386/loader/help.i386 b/sys/boot/i386/loader/help.i386
index 81288250ade0..4e4ec8bb2b27 100644
--- a/sys/boot/i386/loader/help.i386
+++ b/sys/boot/i386/loader/help.i386
@@ -16,6 +16,8 @@
 ################################################################################
 # Tset Snum_ide_disks DSet the number of IDE disks
 
+	NOTE: this variable is deprecated, use root_disk_unit instead.
+
 	set num_ide_disks=<value>
 
 	When booting from a SCSI disk on a system with one or more IDE disks,
@@ -32,3 +34,13 @@
 	be run when the kernel is booted.
 
 ################################################################################
+# Tset Sroot_disk_unit DForce the root disk unit number.
+
+	set root_disk_unit=<value>
+
+	If the code which detects the disk unit number for the root disk is
+	confused, eg. by a mix of SCSI and IDE disks, or IDE disks with
+	gaps in the sequence (eg. no primary slave), the unit number can be
+	forced by setting this variable.
+
+################################################################################