resizable console

How do I make the Xen console automatically resize itself when the terminal window is resized?

On previous UML hosts, when I resized PuTTY, the console resized itself to the window size. On the new Xen host, the console stays at the default size when I resize the terminal window:

root@xxx:~ # stty -a
speed 38400 baud; rows 0; columns 0; line = 0;
..snip..

Suggestions?