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

Effective January 1, 2015, by replacing Section 4.2 Vesting, (a) of the Plan, in its entirety, with the following:

A Participant will, at all times, have a fully vested and nonforfeitable right to the value of the Participant’s Savings Contribution Account, Matching Contribution Account, Rollover Account, and ESOP Account. As described in any Plan supplement adding a Profit Sharing feature, a number of years of service may be required for the Participant to be fully vested in their Profit Sharing Account. If a Participant terminates employment before becoming fully or partially vested in their Profit Sharing Account, the non-vested portion in such account shall be forfeited as of the last day of the Plan Year in which the Participant terminates employment with the Company and all Affiliates. Any forfeitures which arise under the terms of this paragraph shall be used for any of the following: 1) to reinstate the profit sharing contributions of any reemployed Participants pursuant to the terms of the Plan, 2) to reduce employer contributions to the Plan, and 3) to reduce administrative expenses incurred by the Plan. In the case of a Profit Sharing Feature or Retirement Contribution Feature requiring a number of years of service for the Participant to be fully vested in his or her Profit Sharing/Retirement Contribution Account, a Participant who dies while performing qualified military service (as defined in Section 414(u) of the Code) will receive service credit for vesting purposes for the period of qualified military service.

Effective January 1, 2015, by replacing the table in Section D-1-2 Eligibility to Share in the Profit Sharing Feature of Supplement D-1, Provisions Relating to the Profit Sharing Feature for Certain Participating Affiliates, in its entirety, with the following: