Updating my Paperwhite (first gen) from 5.4.4.2 to 5.6.1.1 just reboots it without ac

It happens the same both over the normal wifi update and manually downloading and placing the 5.6.1.1 .bin in the root directory. I select "Update Your Kindle", choose "OK" at the verification prompt, and the Kindle just reboots. Upon checking the firmware version, it's still on 5.4.4.2.
Any suggestions?