Apparent problem with cursor: url(uri);

There appears to be a fault with the CSS Validator.
Using  
cursor: url(cursor.cur);
to display an image as a custom cursor shows as invalid.
the message being
Value Error : cursor Missing comma separator. : url(cursor.cur) url(cursor.cur) 

whereas if I use something like 
cursor: crosshair;

the built in cursors is valid.

Regards
Ian