INSTRUMENT OF AMENDMENT TO THE MDU RESOURCES GROUP, INC. 401(k) RETIREMENT PLAN

The MDU Resources Group, Inc. 401(k) Retirement Plan (as amended and restated March 1, 2011) (the “K-Plan”), is hereby further amended as follows:

Spouse – A “Spouse” means the legally married spouse of a Participant determined in accordance with IRS and/or Department of Labor guidance applicable to the Plan. Prior to June 26, 2013, "Spouse" means only the Participant’s lawful opposite-sex spouse. From June 26, 2013 through September 15, 2013, the Plan also recognizes the marriage of a Participant to a same-sex spouse that was valid in the state where it was entered into provided the Participant is domiciled in a state that recognizes same‑sex marriages. Effective September 16, 2013, the Plan also recognizes the marriage of a Participant to a same-sex spouse that was valid in the state where it was entered into regardless of whether the Participant is domiciled in a state that recognizes same-sex marriages.

IN WITNESS WHEREOF, MDU Resources Group, Inc., as Sponsoring Employer of the Plan, has caused this amendment to be duly executed by a member of the MDU Resources Group, Inc. Employee Benefits Committee (“Committee”) on this 30th day of December, 2014.