Maximum length for optical toslink

Hi all,
I have moved to PC based digital and currently have my PC about 20' away from my DAC, with a 25' optical cable between them...is this a no-no? Is there any reason to believe that my sound quality will suffer as a result? I am considering moving to a Duet...but not for a while.
Also, I do not really have the space to move my computer closer...
thanks for your suggestions.
Byron