How do I set an enumeration value from C

I have a C function that builds a Matlab structure. It has a field that's an enumeration. I've subclassed the enumeration in Matlab from int32. I don't see a way to set an enumeration value in the field from my C function. I've used mxCreateNumericArray() and set the value as if it's an integer, which works, but the class of the field is changed from the enumeration to integer. How do I set an enumeration value so in Matlab, the type of the field remains an enumeration?

Thanks.