Mass. Gen. Laws ch. 184, § 6A

In a limitation of real or personal property to a class described as the ''heirs'' or ''next of kin'' of a person, or described by words of similar import, to take effect in enjoyment upon the happening of an event within the period of the rule against perpetuities, the class shall, unless a contrary intention appears by the instrument creating such limitation, be determined as if such person died at the time of the happening of such event.