Accessibility inconsistency c #

I have the following class that marks me error in the second word Address of the virtual method:

public class Profesor {
        public Profesor() {
        }
        public Profesor(int id, string nombre, string ape1, string ape2) {
            this.id = id;
            this.nombre = nombre;
            this.ape1 = ape1;
            this.ape2 = ape2;
        }
        private int id;
        public virtual int Id {
            get { return id; }
            set { id = value; }
        }
        private String nombre;
        public virtual string Nombre {
            get { return nombre; }
            set { nombre = value; }
        }
        private String ape1;
        public virtual string Ape1 {
            get { return ape1; }
            set { ape1 = value; }
        }
        private String ape2;
        public virtual string Ape2 {
            get { return ape2; }
            set { ape2 = value; }
        }
        private Direccion direccion;
        public virtual Direccion Direccion {
            get { return direccion; }
            set { direccion = value; }
        }

    }

The error says Accessibility inconsistency: The 'Address' property type is less accessible than the 'Teacher.Direction' property. How can I fix it? This is the Address class:

class Direccion {
        public Direccion() {
        }
        public Direccion(int id,String calle, int numero,String poblacion, String provincia) {
            this.id = id;
            this.calle = calle;
            this.numero = numero;
            this.poblacion = poblacion;
            this.provincia = provincia;
        }
        private int id;
        public virtual int Id {
            get { return id; }
            set { id = value; }
        }
        private String calle;
        public virtual String Calle {
            get { return calle; }
            set { calle = value; }
        }
        private int numero;
        public virtual int Numero {
            get { return numero; }
            set { numero = value; }
        }
        private String poblacion;
        public virtual String Poblacion {
            get { return poblacion; }
            set { poblacion = value; }
        }
        private String provincia;
        public virtual String Provincia {
            get { return provincia; }
            set { provincia =value; }
        }
    }