diff --git a/module_dfu/doc/factory_image.rst b/module_dfu/doc/factory_image.rst
index f301c005..bd331d5e 100644
--- a/module_dfu/doc/factory_image.rst
+++ b/module_dfu/doc/factory_image.rst
@@ -1,26 +1,32 @@
 Installing the factory image to the device
 ==========================================
 
-To rebuild the USB audio firmware with the DFU device interface edit the
-device_defines.h file and comment in the #define DFU line.
+The DFU device interface is enabled by default in the XMOS USB Audio framework
+(see ``devicedefines.h``), and the explicitly enabled in each reference design
+by the following line included in the ``customdefines.h`` file of each
+application::
+
+  #define DFU                (1)
 
 Use the XMOS Development Tools to run the command:
 
   ``xflash --boot-partition-size 0x20000 usb_audio.xe``
 
-This programs the factory default firmware image into the flash device. This
-will add a new interface to the device that supports the DFU mechanism.
+This programs the factory default firmware image into the flash device.
+The device will now support the DFU mechanism, and can use it to safely receive
+firmware updates, as well as revert to the factory firmware image when required,
+such as in the event of a failed upgrade attempt.
 
 To use the firmware upgrade mechanism you need to build a firmware upgrade
 image:
 
-#. Edit the ``device_defines.h`` file and change the BCD_DEVICE number for the
-   application.
+#. Edit the ``customdefines.h`` file of the application for the hardware in use,
+   and change the Device Version Number by defining ``BCD_DEVICE``.
 #. Rebuild the application.
 
 To generate the firmware upgrade image run the following command:
 
   ``xflash --upgrade 1 usb_audio.xe 0x20000 -o new_firmware.bin``
 
-You should now have the file ``usb_audio_class1.bin`` which contains the
-firmware for the audio class 1 implementation.
+You should now have the file ``new_firmware.bin`` which contains the
+firmware with the newly specified Device Version Number.