how to make material code field mandatory in VA01

Dear all,

I want to make material code field mandatory while creating sales order (VA01). As of now even if I dont enter material code , and just enter customer code and P.O. number , I am able to save my sales order.

I tried to do it with incompletion log , but could not succeed.

SHD0 could be an option, is there any simpler way out ?

Please suggest.

Regards,