class Base<T> { public virtual void Foo(Base<T> obj) { } } class Derived : Base<Derived> { internal class Base<P> { } } Override method Base<T>.Foo in inheritor class. Wrong code is generated bacause conflicting nested class is disregarded: class Base<T> { public virtual void Foo(Base<T> obj) { } } class Derived : Base<Derived> { public override void Foo(Base<Derived> obj) /* error CS0115: 'Derived.Foo(Derived.Base<Derived>)': no suitable method found to override */ { base.Foo(obj); } internal class Base<T> { } } Expected result: using Base_1 = Base<Derived>; class Base<T> { public virtual void Foo(Base<T> obj) { } } class Derived : Base<Derived> { public override void Foo(Base_1 obj) { base.Foo(obj); } } internal class Base<T> { } }