diff --git a/udev/99-hid.rules b/udev/99-hid.rules
index 5e98cd1..09e7c02 100644
--- a/udev/99-hid.rules
+++ b/udev/99-hid.rules
@@ -22,6 +22,9 @@ KERNEL=="hidraw*", ATTRS{busnum}=="1", ATTRS{idVendor}=="04d8", ATTRS{idProduct}
 # /etc/udev/rules.d and unplug and re-plug your device. This is all that is
 # necessary to see the new permissions. Udev does not have to be restarted.
 
+# Note that the hexadecimal values for VID and PID are case sensitive and
+# must be lower case.
+
 # If you think permissions of 0666 are too loose, then see:
 # http://reactivated.net/writing_udev_rules.html for more information on finer
 # grained permission setting. For example, it might be sufficient to just