undo: changes outside of visible portion of buffer

[Eric Abrahamsen <eric@ericabrahamsen.net>]

I'm trying to undo a fairly large chunk of text deletion, and emacs is
telling me:

undo-more: Changes to be undone are outside visible portion of buffer

I get this no matter where I scroll in the buffer -- it's only about
three screenfuls. I had undo-tree-mode active when I did the deletion,
but I get the same error whether it's active or no.

I'd like this text back, and I don't care if it's not visible! I can't
find any switches that might allow me to circumvent the error -- what
options do I have here?

emacs-version: "24.3.1"

Thanks,
Eric