JUNE 14, 2024

Supplement

SUPPLEMENT DATED JUNE 14, 2024 TO THE STATEMENTS OF ADDITIONAL INFORMATION OF

Morgan Stanley Global Fixed Income Opportunities Fund, dated February 28, 2024, as amended
Morgan Stanley Long Duration Government Opportunities Fund, dated April 29, 2024, as amended
Morgan Stanley Mortgage Securities Trust, dated February 28, 2024, as amended
Morgan Stanley Insight Fund, dated April 30, 2024
Morgan Stanley U.S. Government Money Market Trust, dated May 30, 2024, as amended
(the "Funds")

Richard G. Gould joined the Board of Trustees of each Fund as an Independent Trustee effective June 1, 2024. As a result, all references to 10 Trustees are hereby deleted and replaced with 11 Trustees. In addition, references to the Compliance and Insurance Committee and Equity Investment Committee membership are hereby amended to reflect that Mr. Gould is a member of each such Committee.

The following is hereby added as a new row in the section of the Funds' Statements of Additional Information titled "Management of the Fund—Management Information—Trustees":

Name, Address and Birth Year of Independent Trustee

Position(s) Held with Registrant

Length of Time Served*

Principal Occupation(s) During Past 5 Years and Other Relevant Professional Experience

Number of Funds in Fund Complex Overseen by Independent Trustee

Other Directorships Held by Independent Trustee During Past 5 Years**

Richard G. Gould c/o Morgan, Lewis and Bockius LLP Counsel to the Independent Trustees One State Street Hartford, CT 06103 Birth Year: 1959

Trustee

Since June 2024

Global Chief Executive Officer, CLSA Ltd. (2019-2021); Chief Executive Officer, Americas, CLSA Americas, LLC (2014-2021); Head of Global Sales, Bloomberg Tradebook, Bloomberg LP (2010-2014); Founding Member, Executive Vice President, Information Services Group (2006-2010); Managing Director, Morgan Stanley (1990-2006); Executive Director, International Portfolio Trading & Derivatives, Morgan Stanley (1988-1990); Vice President, International Portfolio Trading & Derivatives, Morgan Stanley (1986-1988; Equity Derivatives Trading, Lehman Brothers (1983-1986)

84

Global Management Committee Member, CLSA (2014-2020); Broking Executive Committee Member, CLSA (2014-2020)

The following is hereby added to the section of the Funds' Statements of Additional Information titled "Management of the Fund—Experience, Qualifications and Attributes":

With over 30 years of global experience in the financial services industry, Mr. Gould brings extensive expertise in managing and developing diverse businesses within financial organizations. Mr. Gould's approach to management combines strategic perspective with deep global operations experience. Throughout his career in finance, he has held executive positions at firms including Lehman Brothers, Morgan Stanley, Information Services Group (ISG), Bloomberg LP, and CLSA Americas (CLSA). Mr. Gould began his career as an equity derivatives options trader at Lehman Brothers. He then transitioned to Morgan Stanley to start its Non-US Derivatives and Global Portfolio trading business, where he eventually became a Managing Director and held a diverse set of senior positions, heading the firm's various business lines in New York, London, and Tokyo. After his tenure with Morgan Stanley, Mr. Gould began a new venture as a Founding Member and Executive Vice President of ISG, a special purpose acquisition company. After successfully taking ISG public, Mr. Gould joined Bloomberg Tradebook as its Head of Global Sales and built a sales organization around the firm's fixed income, equities derivatives, FX products, and logarithmic trading platform. Mr. Gould next held Chairman, CEO, and other executive roles within CLSA and its global affiliates. At CLSA, he provided strategic leadership for the company and its affiliates, establishing and implementing long range goals, strategies, plans, and policies. He was also a member of the CLSA Global Management Committee and the CLSA Broking Executive Committee, further contributing to his governance experience.

Please retain this supplement for future reference.