W I T N E S S E T H:

SIXTH SUPPLEMENTAL INDENTURE (this “Sixth Supplemental Indenture”), dated as of September 30, 2013, among DYNAMIC TOWER SERVICES, INC., a Louisiana corporation and a subsidiary of the Company (as defined below) (“DTS”), GO GREEN SERVICES, LLC, a Texas limited liability company and a subsidiary of the Company (as defined below) (“Go Green” and, together with DTS, the “New Guarantors”), MASTEC, INC., a Florida corporation (the “Company”), and U.S. BANK NATIONAL ASSOCIATION, as trustee under the Indenture referred to below (the “Trustee”).

WHEREAS the Company has heretofore executed and delivered to the Trustee an indenture (as amended, supplemented or otherwise modified, the “Indenture”) dated as of November 10, 2009, providing for (i) the issuance by the Company from time to time of its senior debt securities evidencing its unsecured and unsubordinated indebtedness, in an unlimited aggregate principal amount, in one or more series and (ii) the guaranty of such securities by the guarantors party thereto;

WHEREAS the Company has heretofore supplemented the Indenture by, among other things, executing and delivering to the Trustee (i) the First Supplemental Indenture, dated as of June 5, 2009 (the “First Supplemental Indenture”), by and among the Company, the guarantors party thereto and the Trustee, relating to the Company’s original 4.00% Convertible Senior Notes due 2014 (the “Original 4.00% Senior Convertible Notes”), (ii) the Second Supplemental Indenture, dated as of November 10, 2009 (the “Second Supplemental Indenture”), by and among the Company, the guarantors party thereto and the Trustee, relating to the Company’s original 4.25% Convertible Senior Notes due 2014 (the “Original 4.25% Senior Convertible Notes”), (iii) the Third Supplemental Indenture, dated as of January 11, 2011 (the “Third Supplemental Indenture”), by and among the Company the guarantors party thereto and the Trustee, relating to the Company’s new 4.00% Senior Convertible Notes due 2014 (the “New 4.00% Senior Convertible Notes” and, together with the Original 4.00% Senior Convertible Notes, the “4.00% Senior Convertible Notes”), (iv) the Fourth Supplemental Indenture, dated as of January 11, 2011 (the “Fourth Supplemental Indenture”), by and among the Company, the guarantors party thereto and the Trustee, relating to the Company’s new 4.25% Senior Convertible Notes due 2014 (the “New 4.25% Senior Convertible Notes” and, together with the Original 4.25% Senior Convertible Notes, the “4.25% Senior Convertible Notes”), and (v) the Fifth Supplemental Indenture, dated as of March 18, 2013 (the “Fifth Supplemental Indenture”), by and among the Company, the guarantors party thereto and the Trustee, relating to the Company’s 4.875% Senior Notes due 2023 (the “Senior Notes” and, together with the 4.25% Senior Convertible Notes and the 4.00% Senior Convertible Notes, the “Notes”);

WHEREAS Section 4.04 of the First Supplemental Indenture, Section 4.04 of the Second Supplemental Indenture, Section 4.04 of the Third Supplemental Indenture, Section 4.04 of the Fourth Supplemental Indenture and Section 4.15 of the Fifth Supplemental Indenture each provide that under certain circumstances, the Company is required to cause each of the New Guarantors to execute and deliver to the Trustee a supplemental indenture pursuant to which each of the New Guarantors shall unconditionally guarantee all the Company’s obligations under the Notes and the Indenture on the terms and conditions set forth herein (the “Guarantee”); and

WHEREAS pursuant to Section 901 of the Indenture, Section 6.01 of the First Supplemental Indenture, Section 6.01 of the Second Supplemental Indenture, Section 6.01 of the Third Supplemental Indenture, Section 6.01 of the Fourth Supplemental Indenture and Section 9.01 of the Fifth Supplemental Indenture, the Trustee, the Company and the New Guarantors are each authorized to execute and deliver this Supplemental Indenture.

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