Exhibit 10.3

Execution Version

COLLATERAL TRUST JOINDER – ADDITIONAL GRANTOR

Reference is made to the Collateral Trust Agreement, dated as of October 3, 2016 (as amended, supplemented, amended and restated or otherwise modified and in effect from time to time, the “Collateral Trust Agreement”), among Vistra Operations Company LLC (f/k/a TEX Operations Company LLC, the “Company”), the other Grantors from time to time party thereto, Railroad Commission of Texas, as First-Out Representative (as defined therein), Credit Suisse AG, Cayman Islands Branch (as successor agent to Deutsche Bank AG New York Branch), as Senior Credit Agreement Agent (as defined therein), and Delaware Trust Company, as Collateral Trustee. Capitalized terms used but not otherwise defined herein have the meanings assigned to them in the Collateral Trust Agreement. This Collateral Trust Joinder is being executed and delivered pursuant to Section 7.19 of the Collateral Trust Agreement.

1. Joinder. Each of the undersigned entities (collectively, the “Additional Grantors” and each an “Additional Grantor”), hereby agree to become party as a Grantor under the Collateral Trust Agreement for all purposes thereof on the terms set forth therein, and to be bound by the terms of the Collateral Trust Agreement as fully as if the undersigned had executed and delivered the Collateral Trust Agreement as of the date thereof.

2. Security Documents. Each Additional Grantor has become party to all of the Security Documents that provide, for the benefit of all of the Priority Lien Secured Parties liens and security interests in such assets of the Additional Grantor as are required pursuant to the Priority Lien Documents.

2. Governing Law and Miscellaneous Provisions. The provisions of Article 7 of the Collateral Trust Agreement will apply with like effect to this Collateral Trust Joinder.

C-1

IN WITNESS WHEREOF, the parties hereto have caused this Collateral Trust Joinder to be executed by their respective officers or representatives as of June 14, 2018.

[Signature Page to Joinder to Collateral Trust Agreement]

The Collateral Trustee hereby acknowledges receipt of this Collateral Trust Joinder and agrees to act as Collateral Trustee with respect to the Collateral pledged by the new Grantors:

[Signature Page to Joinder to Collateral Trust Agreement]