Twitter’s board of directors has adopted a limited-term shareholder rights plan called a “poison pill” that could make it harder for Elon Musk to acquire the company.

The “poison pill” provision, announced in a press release Friday, preserves the right for Twitter shareholders other than Musk to acquire more shares of the company at a relatively inexpensive price, effectively diluting Musk’s stake. The provision will be triggered if Musk (or any other investor) acquires more than 15% of the company’s shares. Musk currently owns around 9% of Twitter’s shares.

The move marks an effort by Twitter’s board to wrest back some control in the deal after Musk’s stunning acquisition offer. The poison pill ā€” a corporate anti-takeover defense mechanism ā€” won’t necessarily stop Musk’s bid in its tracks, but it could make buying the company more expensive or force Musk to the negotiating table with the board.

“The Rights Plan will reduce the likelihood that any entity, person or group gains control of Twitter through open market accumulation without paying all shareholders an appropriate control premium or without providing the Board sufficient time to make informed judgments and take actions that are in the best interests of shareholders,” the company said in its statement.