Conn. Gen. Stat. § 12-393: Credit against tax on future interests.

If, after the payment of the tax under the provisions of this chapter, there becomes payable a tax under the provisions of the succession tax law in force at the date of the decedent's death upon any future interest in any property owned by such decedent or subject to such tax as a part of or in connection with his estate, the tax paid under the provisions of this chapter shall be credited against such succession tax, but the amount so credited shall not in any event exceed the amount of the tax on such future interest.