Production never reduced - java cup warning

I'm facing this error:

Production "mulop ::= MUL " never reduced

I'm using java cup, and I'm still new to the whole thing.

Grammar looks like this:

Addop  = "+" | "‐".
Mulop  = "*" | "/" | "%".

and my .cup file looks like this:

terminal PLUS, MINUS, MUL, DIV, MOD ;
non terminal addop, mulop ;

addop ::= PLUS | MINUS ;
mulop ::= MUL | DIV | MOD ;

When I run the file, I get this warning:

Warning : *** Production "mulop ::= MOD " never reduced
Warning : *** Production "mulop ::= DIV " never reduced
Warning : *** Production "mulop ::= MUL " never reduced

Can anyone help with this?