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, effective March 15, 2015, unless otherwise indicated as follows:

For purposes of this Supplement, an “Active Employee” means an employee who is still on the payroll, has been temporarily laid off, or who terminated employment due to Disability, death, or after attaining age 60 during such Plan Year, but does not mean an employee whose employment has been terminated effective on or before December 31 of that Plan Year. In addition, for purposes of applying the requirement of completing 1,000 Hours of Service for the Plan Year, such requirement shall not apply to employees terminating after attaining age 60 provided they are not terminated for cause.

In order to share in the allocation of any Retirement Contribution made by a Supplement D-2 Company pursuant to Paragraph 3 below for a given Plan Year, Eligible Employees described above must be credited with 1,000 Hours of Service (prorated for the Plan Year in which the Retirement Contribution Feature becomes effective) in that Plan Year and must not be covered by a collectively bargained unit to which the Retirement Contribution has not been extended. However, if the Participant’s failure to be credited with 1,000 Hours of Service in that Plan Year is due to the Participant’s (i) Disability; (ii) death; or (iii) termination of employment on or after attaining age 60 during such Plan Year provided the Participant is not terminated for cause, such Participant shall nevertheless be entitled to share in the allocation of the Retirement Contributions for such Plan Year. Any Participant who is not a Highly Compensated Employee who has met the above eligibility requirements as of June 30 each Plan Year shall receive a pro-rata allocation mid-year based on compensation paid through June 30. The final annual allocation shall be reduced by any such mid‑year allocation. Participants who meet the requirements of this paragraph are referred to herein as “Supplement D-2 Participants.”

In order to share in the allocation of any Retirement Contribution made by a Supplement D-6 Company pursuant to Paragraph 3 below for a given Plan Year, Eligible Employees described above must be credited with 1,000 Hours of Service in that Plan Year; provided, however, that if the Participant’s failure to be credited with 1,000 Hours of Service in that Plan Year is due to the Participant’s (i) Disability; (ii) death; or (iii) termination of employment on or after attaining age 60 during such Plan Year provided the Participant is not terminated for cause, such Participant shall nevertheless be entitled to share in the allocation of the Retirement Contribution for such Plan Year. Any Participant who is not a Highly Compensated Employee who has met the above eligibility requirements as of June 30 each Plan Year shall receive a pro-rata allocation mid-year based on compensation paid through June 30. The final annual allocation shall be reduced by any such mid‑year allocation. Participants who meet the requirements of this paragraph are referred to herein as “Supplement D-6 Participants.”

In order to share in the allocation of any Retirement Contribution made by a Supplement D-6A Company pursuant to Paragraph 3 below for a given Plan Year, Eligible Employees described above must be credited with 1,000 Hours of Service in that Plan Year; provided, however, that if the Participant’s failure to be credited with 1,000 Hours of Service in the Plan Year is due to the Participant’s (i) Disability; (ii) death; or (iii) termination of employment on or after attaining age 60 during such Plan Year provided the Participant is not terminated for cause, such Participant shall nevertheless be entitled to a Retirement Contribution for such Plan Year. Any Participant who is not a Highly Compensated Employee who has met the above eligibility requirements as of June 30 each Plan Year shall receive a pro-rata allocation mid-year based on compensation paid through June 30. The final annual allocation shall be reduced by any such mid‑year allocation. Participants who meet the requirements of this paragraph are referred to herein as “Supplement D-6A Participants.”

“In order to share in the allocation of the Retirement Contribution made by DPR for any Plan Year, Eligible Employees must be credited with 1,000 Hours of Service (prorated for the Plan Year in which the Retirement Contribution becomes effective) in that Plan Year; provided, however, that if the Participant’s failure to be credited with 1,000 Hours of Service in the Plan Year is due to the Participant’s (i) Disability; (ii) death; or (iii) termination of employment on or after attaining age 60 during such Plan Year, provided the Participant is not terminated for cause, such Participant shall nevertheless be entitled to a Retirement Contribution for such Plan Year. Any Participant who is not a Highly Compensated Employee who has met the above eligibility requirements as of June 30 each Plan Year shall receive a pro-rata allocation mid-year based on compensation paid through June 30. The final annual allocation shall be reduced by any such mid-year allocation. Participants who meet the requirements of this paragraph are referred to herein as “Supplement D-8 Participants.”

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 13th day of March, 2015.