c# generics error: The constraints for type parameter 'T' of method ...?

Getting the following error:

Error 1 The constraints for type parameter 'T' of method
'genericstuff.Models.MyClass.GetCount<T>(string)' must match the constraints for type
parameter 'T' of interface method 'genericstuff.IMyClass.GetCount<T>(string)'. Consider
using an explicit interface implementation instead.

Class:

 public class MyClass : IMyClass
 {
     public int GetCount<T>(string filter)
     where T : class
       {
        NorthwindEntities db = new NorthwindEntities();
        return db.CreateObjectSet<T>().Where(filter).Count();
       }
 }

Interface:

public interface IMyClass
{
    int GetCount<T>(string filter);
}