diff --git a/etc/rc.d/gbde b/etc/rc.d/gbde
index 4ab9abc8d367..612fd7e255a8 100644
--- a/etc/rc.d/gbde
+++ b/etc/rc.d/gbde
@@ -18,6 +18,8 @@ start_cmd="gbde_start"
 stop_cmd="gbde_stop"
 
 # Change every ${_src} in ${_str} to ${_dst}.
+# We cannot use tr(1), sed(1) nor awk(1) here, because this script is executed
+# before /usr is mounted.
 local_tr()
 {
 	_str=$1