(Bloomberg) -- Members of the Walton family have sold 16.7 million shares of Walmart Inc. this year as they try to keep their stake in the world’s biggest retailer from ballooning amid the company’s stock buybacks.

The Walton Family Holdings Trust sold $430 million worth over the past week, taking their total sales to almost $2.1 billion since Jan. 1, according to Securities and Exchange Commission filings. The notifications were filed on behalf of second-generation family members Alice, Rob and Jim Walton.

The family owns about half of the retailer’s outstanding shares through the trust and their main investment vehicle, Walton Enterprises.

The trust has been their main vehicle for share sales in recent years. They shifted 194 million shares to it in 2015 -- almost all of which they subsequently sold -- and moved 415 million more last year.

The recent sales “are consistent with the family’s effort to maintain an appropriate balance of family and non-family ownership of Walmart by offsetting possible increases in its ownership percentage over time and helping fund charitable contributions,” said Randy Hargrove, a spokesman for the Bentonville, Arkansas-based company.

Buyback Plan

Walmart has bought back $37.4 billion of shares since it started a repurchasing program in 2015, according to data compiled by Bloomberg.

During that time, the stock has risen 64%. That’s helped lift the family’s combined fortune to $216 billion, according to the Bloomberg Billionaires Index, about three-quarters of which is tied to Walmart stock.

The buybacks have helped shrink the number of Walmart’s outstanding shares by 13%, meaning the Waltons’ stake would have crept over 50% without them selling. Walton Enterprises hasn’t been acquiring common stock, Hargrove said.

U.S. public company insiders offloaded shares worth $29.4 billion this year through May, according to data compiled by Bloomberg. Among those stepping up sales are some of world’s richest corporate insiders.

Jeff Bezos has cashed in $6.7 billion of Amazon.com Inc. stock this year, while Leslie Wexner has sold $500 million worth of L Brands Inc. shares.

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