Change Gnucash GUI Font on mac?

[Aaron Johns]

Hi there, I hope I have used the right address for support questions on Gnucash, thanks in advance for any assistance. I upgraded my mac to OS X (10.10) Yosemite yesterday and the font in the main window has changed (see screenshot attached). Is there a setting somewhere that I can choose a new font as this one is very hard for my poor old eyes to read. :)
Thanks.