Company Order, dated September 16, 2019, establishing the Notes

Exhibit 4.3

AMEREN CORPORATION

Company Order

September 16, 2019

The Bank of New York Mellon Trust Company, N.A.,

as Trustee

2 North LaSalle Street, Suite 1020

Chicago, Illinois 60602

Ladies and Gentlemen:

Application is hereby made to The Bank of New York Mellon Trust Company, N.A., a national banking association, as successor trustee (the “Trustee”), under the Indenture, dated as of December 1, 2001, as amended and supplemented (the “Indenture”), between Ameren Corporation, a Missouri corporation (the “Company”), and the Trustee for the authentication and delivery of $450,000,000 aggregate principal amount of the Company’s 2.50% Senior Notes due 2024 (the “Notes”), pursuant to the provisions of Article II of the Indenture. The Company, at any time and from time to time, without the consent of the holders of the Notes, may deliver additional Notes of the same series executed by the Company to the Trustee for authentication, having the same terms and conditions (including the same CUSIP number) as the Notes authenticated pursuant hereto in all respects, except for the date of original issuance, the offering price, and if applicable, the initial interest accrual date and the initial interest payment date. Such additional Notes shall be part of the same series as the Notes authenticated pursuant hereto. All capitalized terms not defined herein that are defined in the Indenture shall have the same meaning as used in the Indenture.

The Notes will be issued in the form of a Global Note registered in the name of Cede & Co. (as nominee for The Depository Trust Company (“DTC”), New York, New York, which will act as the Depositary for each Global Note). Pursuant to Section 2.05(c) of the Indenture, the Notes will have the terms set forth in the form of Global Note attached hereto as Exhibit A (which terms are incorporated by reference in this Company Order). The Global Notes shall bear the depositary legend in substantially the form set forth in Exhibit A attached hereto. The Notes will be issued only in denominations of $2,000 and in integral multiples of $1,000 in excess thereof.

In connection with this Company Order, there are delivered to you herewith the following:

The Global Note representing the Notes is to be held for delivery through the facilities of DTC to BofA Securities, Inc. on behalf of the several underwriters thereof, against payment therefor at the closing in respect of the sale thereof, such closing to be held at 10:00 a.m., New York time, September 16, 2019, at the offices of Morgan, Lewis & Bockius LLP, 101 Park Avenue, New York, New York 10178. You are hereby instructed to authenticate the Global Note representing the Notes in the name of CEDE & Co. as registered holder and to hold it as custodian for DTC.

Please acknowledge receipt of the Global Note representing the Notes, the instructions referred to above and the supporting documentation pursuant to the Indenture referred to above.

Company Signature Page to Company Order

Receipt from the Company of the Global Note representing the Notes, the instructions referred to above and the supporting documentation pursuant to the Indenture in connection with the authentication and delivery of the Notes is hereby acknowledged.

Trustee Signature Page to Company Order