compiler says SaveChanges is not recognized

using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;

namespace Treehouse.CodeChallenges
{
    public static class Repository
    {
        public static List<Course> GetCourses()
        {
            using (var context = new Context())
            {
                return context.Courses
                              .OrderBy(c => c.Teacher.LastName)
                              .ThenBy(c => c.Teacher.FirstName)
                              .ToList();
            }
        }

        public static List<Course> GetCoursesByTeacher(string lastName)
        {
            using (var context = new Context())
            {
                return context.Courses
                              .Where(c => c.Teacher.LastName == lastName)
                              .ToList();
            }
        }

        public static Course GetCourse(int id)
        {
            using (var context = new Context())
            {
                return context.Courses
                              .Include(c => c.Teacher)
                              .SingleOrDefault(c => c.Id == id);
            }
        }

        public static void AddCourse(Course course)
        {
            // TODO
            using (var context = new Context())
            {
                return context.Courses
                              .Add(course)
                              .SaveChanges();
            }
        }
    }
}