OTA DFU, bootloader-only update gives "DFU File Error"

I am testing OTA DFU using NRF toolbox on Android. I have no problem updating my application using a zip file generated with nrfutil.

nrfutil.exe pkg generate --application nrf52832_xxaa.hex --key-file priv.pem --hw-version 52 --sd-req 0x9D --application-version 0x02 application.zip

  1. Android nRF Toolbox
  2. Select File-> Distribution Packet (ZIP)
  3. File is selected.
  4. Select Scope -> Application Only
  5. Select Device - BootloaderBLE
  6. Upload -> Works fine!

However I would like to be able to update my bootloader OTA. I generate a zip file in a similar way from the bootloader .hex file.

nrfutil.exe pkg generate --bootloader bootloader0_2.hex --key-file priv.pem --hw-version 52 --sd-req 0x9D --bootloader-version 0x0000001 bootloader0_2.zip

  1. Android nRF Toolbox
  2. Select File -> Distribution Packet (ZIP)
  3. File is selected
  4. Select Scope -> System Components only
  5. Select Device - Bootloader BLE
  6. Press upload -> "Upload Failed: DFU File Error" appears instantly.

Am I correct in assuming that the bootloader itself can be updated in this way via OTA DFU? Or do I need to update the bootloader by connecting to the application itself? I was under the impression that the bootloader could update itself.