SUPPLEMENT TO PROSPECTUS
The date of this supplement is November 28, 2014.

MFS® U.S. Government Money Market Fund

(formerly MFS® Money Market Fund)

Effective July 1, 2014, the name of the fund is changed to MFS® U.S. Government Money Market Fund.

Effective July 1, 2014, the sub-section entitled “Principal Investment Strategies” beneath the main heading “Summary of Key Information” is restated in its entirety as follows:

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund’s investment adviser) normally invests at least 80% of the fund’s net assets in U.S. Government money market instruments and repurchase agreements collateralized by U.S. Government securities.

In buying and selling investments for the fund, MFS seeks to comply with Securities and Exchange Commission rules for money market funds regarding credit quality, diversification, liquidity, and maturity. MFS stresses maintaining a stable $1.00 share price, liquidity, and income.

Effective November 28, 2014, the sub-section entitled “Principal Risks” beneath the main heading “Summary of Key Information” is restated in its entirety as follows:

Principal Risks

Although the fund seeks to preserve the value of your investment at $1.00 per share, the fund may not achieve its objective and you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.

The principal risks of investing in the fund are:

Issuer Focus Risk: The fund’s performance could be more volatile than the performance of more diversified funds.

Investment Selection Risk: MFS’ investment analysis and its selection of investments may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests.

Counterparty and Third Party Risk: Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty’s or third party’s ability to perform in accordance with the terms of the transaction.

Effective July 1, 2014, the sub-section entitled “Principal Investment Strategies” beneath the main heading “Investment Objective, Strategies, and Risks” is restated in its entirety as follows:

Principal Investment Strategies

MFS normally invests at least 80% of the fund’s net assets in U.S. Government money market instruments and repurchase agreements collateralized by U.S. Government securities.

Effective September 1, 2014, the sub-section entitled “Principal Investment Types” beneath the main heading “Investment Objective, Strategies, and Risks” is restated in its entirety as follows:

Principal Investment Types

The principal investment types in which the fund may invest are:

Money Market Instruments: Money market instruments are high-quality, short-term instruments that pay a fixed, variable, or floating interest rate. Money market instruments include bank certificates of deposit and other bank obligations of U.S. and foreign banks; notes, commercial paper, asset-backed securities of U.S. and foreign issuers; U.S. and foreign government securities; and municipal instruments.

U.S. Government Securities: U.S. Government securities are securities issued or guaranteed as to the payment of principal and interest by the U.S. Treasury, by an agency or instrumentality of the U.S. Government, or by a U.S. Government-sponsored entity. Certain U.S. Government securities are not supported as to the payment of principal and interest by the full faith and credit of the U.S. Treasury or the ability to borrow from the U.S. Treasury. Some U.S. Government securities are supported as to the payment of principal and interest only by the credit of the entity issuing or guaranteeing the security. U.S. Government securities include mortgage-backed securities and other types of asset-backed securities issued or guaranteed by the U.S. Treasury, by an agency or instrumentality of the U.S. Government, or by a U.S. Government-sponsored entity.

Repurchase Agreements: Repurchase agreements are agreements to buy a security from a third party at one price, with simultaneous agreements to sell it back to the third party at an agreed-upon price.

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MFS U.S. Government Money Market Fund

Effective September 1, 2014, the sub-section entitled “Principal Risks” beneath the main heading “Investment Objective, Strategies, and Risks” is restated in its entirety as follows:

Principal Risks

The fund’s yield will change daily based on changes in interest rates and other market, economic, industry, political, regulatory, geopolitical, and other conditions. Although the fund seeks to preserve the value of your investment at $1.00 per share, the fund may not achieve its objective and you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.

The principal risks of investing in the fund are:

Interest Rate, Credit, Redemption, and Liquidity Risk: Although MFS seeks to maintain a stable $1.00 share price for the fund, there is no guarantee that it will be able to do so. A major or unexpected increase in interest rates, a decline in the credit quality of an issuer or entity providing credit support, large or frequent redemptions, or an inactive trading market for money market instruments could cause the fund’s share price to decrease to below $1.00. The value of a money market instrument can also decline in response to changes in the financial condition of the issuer or borrower, changes in specific market, economic, industry, political, regulatory, geopolitical, and other conditions that affect a particular type of instrument, issuer, or borrower, and changes in general market, economic, industry, political, regulatory, geopolitical, and other conditions.

Issuer Focus Risk: Because MFS may invest a relatively large percentage of the fund’s assets in a single issuer or small number of issuers, the fund’s performance could be closely tied to that one issuer or those issuers, and could be more volatile than the performance of more diversified funds.

Counterparty and Third Party Risk: Transactions involving a counterparty other than the issuer of the instrument, including clearing organizations, or a third party responsible for servicing the instrument or effecting the transaction, are subject to the credit risk of the counterparty or third party, and to the counterparty’s or third party’s ability to perform in accordance with the terms of the transaction.

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