How to avoid DateTime truncation with composite key in NHibernate?

Question

I have the following (using Fluent NHibernate):

public class BuildAuditMap : ClassMap<BuildAudit>
{
    public BuildAuditMap()
    {
        Table("BUILD_AUDIT");

        CompositeId()
            .KeyProperty(x => x.AuditDate, c => c.ColumnName("AUDIT_DATE"))
            .KeyProperty(x => x.PersonId, c => c.ColumnName("PERSON_ID"));


        Map(m => m.BuildType).Column("BUILD_TYPE");
    }
}

When I persist this, the AUDIT_DATE column features truncated milliseconds. I have read the solutions on how to deal with this when it's a regular mapped column. I can't seem to find a way to make it work for a composite key column. How can I preserve the milliseconds for this column?