Article 38
Rules in a treaty becoming binding on third States or
third organizations through international custom
Nothing in articles 34 to 37 precludes a rule set forth in a treaty from becoming binding upon a third State or a third organization as a customary rule of international law, recognized as such.
PART IV.
AMENDMENT AND MODIFICATION OF TREATIES
Article 39
General rule regarding the amendment of treaties
1. A treaty may be amended by agreement between the parties. The rules laid down in Part II
apply to such an agreement except insofar as the treaty may otherwise provide.
2. The consent of an international organization to an agreement provided for in paragraph 1 shall be governed by the rules of that organization.
Article 40
Amendment of multilateral treaties
1.Unless the treaty otherwise provides, the amendment of multilateral treaties shall be governed by the following paragraphs.
2. Any proposal to amend a multilateral treaty as between all the parties must be notified to all the contracting States and all the contracting organizations, each one of which shall have the right to take part in:
(a) the decision as to the action to be taken in regard to such proposal;
(b) the negotiation and conclusion of any agreement for the amendment of the treaty.
3.Every State or international organization entitled to become a party to the treaty shall also be entitled to become a party to the treaty as amended.
4. The amending agreement does not bind any State or international organization already a party to the treaty which does not become a party to the amending agreement; article 30, paragraph 4 (b), applies in relation to such State or organization.
5. Any State or international organization which becomes a party to the treaty after the entry into force of the amending agreement shall, failing an expression of a different intention by that State or that organization:
(a) be considered as a party to the treaty as amended; and
