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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

Current Report

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported):  September 2, 2015

(Exact name of registrant as specified in its charter)

37 South River Street

Aurora, Illinois  60507

(Address of principal executive offices) (Zip code)

(630) 892-0202

(Registrant’s telephone number, including area code)

N/A

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

☐Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 1.01.  Entry into a Material Definitive Agreement.

On September 2, 2015, Old Second Bancorp, Inc. (the “Company”) and Old Second National Bank, as rights agent (the “Rights Agent”), entered into a Second Amendment to Amended and Restated Rights Agreement and Tax Benefits Preservation Plan (the “Amendment”), which amended the Amended and Restated Rights Agreement and Tax Benefits Preservation Plan, dated as of September 12, 2012, between the Company and the Rights Agent (as amended, the “Tax Benefits Plan”).

The Amendment, which will be submitted to the Company’s stockholders for ratification at the Company’s 2016 annual meeting, extended the final expiration date of the Tax Benefits Plan from September 12, 2015 to September 12, 2018.

The foregoing summary is qualified in its entirety by the terms and conditions of the Amendment, which is filed herewith as Exhibit 4.1 and is incorporated herein by reference.

Item 3.03  Material Modification to Rights of Security Holders.

Item 1.01 above is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

EXHIBIT INDEX