And a "negative increase" is what, exactly?

One of my readers spotted this piece of brain-frying copy, from "Inflation punctures deflation fears", an article by Krishna Guha in the usually crystal clear FT:

"The danger is deflation defined as a sustained negative rate of underlying domestic price increases."

Huh? Any economists out there got any idea what this means? Am I being too simplistic to think "falling prices" would have been a better way of putting it?