Mandatory File Attribute?

[JB2011]

I'm using Zen Cart 1.3.9h and have added a file upload attribute to a product.

However I cannot work out how to set it to mandatory and was hoping that someone could kindly point me out to a solution.

Perhaps it is not possible out of the box but there must be some sort of jiggery pokery I can do somewhere in the code.

Thanks in advance for your consideration.

[JB2011]

It's OK- this can be closed as I found the module!