Periods in userids

[Rich F. Ronston]

Hello
I have a question about the acceptable syntax of userids in the sudoers file. 
We use NIS and our userid convention is first.lastname. When I enter a
userid that conforms to this standard in the sudoers file,
write and quit, it chokes and throws a syntax error for that line. I tried
the escape sequence/delimiters, but to no avail. Anyone have experience with this or a recommendation?
Thanks for your help

We are running version 1.5.4p1