Interface declaration together with generic constraints

Basic C# syntax question:

So I have this class

public class BrandQuery<T> : Query<T> where T : Ad
{
  //...
}

How do I specify that BrandQuery implements an interface, say IDisposable ?

This is obviously the wrong way:

public class BrandQuery<T> : Query<T> where T : Ad, IDisposable
{
  //...
}

because that would only put a generic constraint on T.