Exhibit 4.3

FIFTH SUPPLEMENTAL INDENTURE

FIFTH SUPPLEMENTAL INDENTURE (this “Supplemental Indenture”) dated as of August 13, 2013 among Pinnacle Entertainment, Inc. (the “Company”), the entities listed on Appendix A hereto (the “Guarantying Subsidiaries”), each a subsidiary of the Company, the other Guarantors (as defined in the Indenture referred to herein) and Wilmington Trust, National Association (as successor by merger to Wilmington Trust FSB), as trustee under the Indenture referred to below (the “Trustee”).

W I T N E S S E T H

WHEREAS, Ameristar Casinos, Inc. (“Ameristar”) and the guarantors party thereto have heretofore executed and delivered to the Trustee an indenture, dated as of April 14, 2011, providing for the issuance of Ameristar’s 7.50% Senior Notes due 2021 (the “Notes”), as amended and supplemented by (i) that Supplemental Indenture dated as of February 23, 2012, by and among Ameristar, the Guarantors party thereto and the Trustee, (ii) that Second Supplemental Indenture dated as of April 26, 2012, by and among Ameristar, the Guarantors party thereto and the Trustee, (iii) that Third Supplemental Indenture dated as of July 18, 2012, by and among Ameristar, the Guarantors party thereto and the Trustee and (iv) that Fourth Supplemental Indenture dated as of April 2, 2013, by and among Ameristar, the Guarantors party thereto and the Trustee (as amended and supplemented, the “Indenture”);

WHEREAS, on the date hereof, the Company consummated its acquisition (the “Acquisition”) of Ameristar by merging a wholly owned subsidiary of the Company with and into Ameristar, and immediately thereafter merging Ameristar with and into the Company, with the Company continuing as the surviving entity, pursuant to that certain Agreement and Plan of Merger, dated as of December 20, 2012, as amended by the First Amendment, entered into on February 1, 2013, and the Second Amendment, entered into on March 31, 2013, among the Company, Ameristar, PNK Holdings, Inc. and PNK Development 32, Inc.; and

WHEREAS, pursuant to this Supplemental Indenture and in connection with the Acquisition the Company will expressly assume the due and punctual payment of the principal of, and premium, if any, and interest on all of the Notes and the performance of every covenant of the Notes and the Indenture on the part of Ameristar to be performed and observed, and the Guarantying Subsidiaries will unconditionally guarantee all of Ameristar’s obligations under the Notes and the Indenture (the “Guaranty”), all in accordance with this Supplemental Indenture and the Indenture;

WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee is authorized to execute and deliver this Supplemental Indenture; and

NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt of which is hereby acknowledged, the Company, the Guarantying Subsidiaries and the Trustee mutually covenant and agree for the equal and ratable benefit of the Holders of the Notes as follows:

1. CAPITALIZED TERMS. Capitalized terms used herein without definition shall have the meanings assigned to them in the Indenture.

2. AGREEMENT TO ASSUME OBLIGATIONS. The Company hereby agrees to assume the due and punctual payment of the principal of, and premium, if any, and interest on all of the Notes and the performance of every covenant of the Notes and the Indenture on the part of Ameristar to be performed and observed and to join and become a party to and be bound by all other applicable provisions of the

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Indenture and the Notes. Every reference to Ameristar in the Indenture and the Notes shall be amended to be a reference to the Company.

3. AGREEMENT TO GUARANTY. Each of the Guarantying Subsidiaries hereby agrees to provide an unconditional Guaranty on the terms and subject to the conditions set forth in the Guaranty and in the Indenture including but not limited to Article 11 thereof (which is hereby incorporated by reference).

4. UNRESTRICTED SUBSIDIARIES. The Board of Directors of the Company has designated each subsidiary listed on Appendix B as an Unrestricted Subsidiary under the Indenture.

5. NO RECOURSE AGAINST OTHERS. No past, present or future director, officer, employee, agent, manager, partner, member, incorporator or stockholder of either of the Guarantying Subsidiaries (or of any stockholder of the Company), as such, shall have any liability for any obligations of the Company or such Guarantying Subsidiary under the Notes, any Guarantees, the Indenture or this Supplemental Indenture or for any claim based on, in respect of, or by reason of, such obligations or their creation. Each Holder of the Notes by accepting a Note waives and releases all such liability. The waiver and release are part of the consideration for issuance of the Notes.

6. NEW YORK LAW TO GOVERN. THE INTERNAL LAW OF THE STATE OF NEW YORK SHALL GOVERN AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

7. COUNTERPARTS. The parties may sign any number of copies of this Supplemental Indenture. Each signed copy shall be an original, but all of such executed copies together shall represent the same agreement.

8. EFFECT OF HEADINGS. The Section headings herein are for convenience only and shall not affect the construction hereof.

9. THE TRUSTEE. The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Supplemental Indenture or for or in respect of the recitals contained herein, all of which recitals are made solely by the Company and the Guarantying Subsidiaries.

[Signature page follows.]

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IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed, all as of the date first above written.

APPENDIX A

List of Guarantying Subsidiaries

APPENDIX B

List of Unrestricted Subsidiaries