public class MyClass1 { public virtual object Copy() { return this.MemberwiseClone(); } } public class MyClass2 : MyClass1 { public new virtual MyClass1 Copy() { return (MyClass1)this.MemberwiseClone(); } } public class MyClass3 : MyClass2 { bool m_Copied = false; public override MyClass1 Copy() // <-- ERROR: cannot change return type when overriding method { m_Copied = true; return (MyClass2)this.MemberwiseClone(); } }