using Guid as PK with EF4 Code First

I have this class and table:

public class Foo
{
public Guid Id {get;set;}
public string Name {get;set;}   
}

create table Foo
(
id uniqueidentifier primary KEY DEFAULT (newsequentialid()),
name nvarchar(255)
)

the problem is that when i try to save new foo the first one goes with the 0000-000-00 ... id and the second also, so I get constraint exception

anybody knows a fix ?