DateTime of 24 hours former ?

[C# Programming]

Hi.

I'm gonna take the DateTime of 24 hours former with C# , I've written below code :

DateTime _24HoursFormer
{
get { return new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day - 1, DateTime.Now.Hour, DateTime.Now.Minute, DateTime.Now.Second); }
}

But whenever DateTime.Now.Day equals 1, it throws an Exception !!

Could you guide me ?
Thanks.