EXHIBIT NO. 99.(a) 46

MFS SERIES TRUST X

CERTIFICATION OF AMENDMENT

TO THE DECLARATION OF TRUST

REDESIGNATION OF SERIES

 Pursuant to Sections 6.11 and 9.3(a) of the Amended and Restated Declaration of Trust dated December 16, 2004, as amended (the “Declaration”), of MFS Series Trust X, a business trust organized under the laws of The Commonwealth of Massachusetts (the “Trust”), the undersigned, constituting a majority of the Trustees of the Trust, hereby redesignate an existing series of Shares (as defined in the Declaration) as follows:

The series designated as MFS International Large Cap Value Fund shall be redesignated as MFS International Value Fund.

 Pursuant to Section 10.1 of the Declaration, this redesignation of series of Shares shall be effective on or about August 1, 2026.

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 IN WITNESS WHEREOF, a majority of the Trustees of the Trust have executed this amendment, in one or more counterparts, all constituting a single instrument, as an instrument under seal in The Commonwealth of Massachusetts, as of August 1, 2026 and further certify, as provided by the provisions of Section 9.3(c) of the Declaration, that this amendment was duly adopted by the undersigned in accordance with Section 9.3(a) of the Declaration.

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