OLD SECOND BANCORP INC — Director's Dealing 2026

Feb 24, 2026

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: OLD SECOND BANCORP INC (OSBC)
CIK: 0000357173
Period of Report: 2026-02-17

Reporting Person: Gartelmann Richard A JR (N/A)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2026-02-17	Restricted Stock Units	A	5912	—	Acquired	26464	Direct
2026-02-21	Restricted Stock Units	F	894	$20.57	Disposed	23879	Direct

Holdings (Non-Derivative)

Security	Shares	Ownership
Old Second Bancorp, Inc. Common Stock	1691	Direct
Old Second Bancorp, Inc. Common Stock	24874	Direct
Old Second Bancorp, Inc. Common Stock	12563	Indirect

Footnotes

F1: Each restricted stock unit represents a contingent right to receive one share of common stock. The reporting person was granted 5,912 restricted stock units on the date of the grant, 2,956 of which are time-based restricted stock units that vest on the third anniversary of the grant date, and 2,956 of which are performance-based restricted stock units that may vest and convert to shares within a range from 0% to 175% of the underlying performance-based restricted stock units originally awarded, depending on our compensation committee approved performance metrics. Vested shares, if any, will be delivered to the reporting person in 3 to 5 business days from the date of vesting.

F2: Represents shares withheld by the issuer to satisfy applicable tax withholding obligations in connection with the vesting of 2,585 previously reported time-based restricted stock units, the remaining shares of which were issued and added to the reporting person's common stock holdings.

F3: These shares are held in Mr. Gartelmann's name outright.