Wendy’s rejected a $1.4 billion buyout offer from an activist investor, saying Thursday that the bid was too low, and it adopted a “poison pill” plan that would make it more difficult to engineer a hostile takeover of the company.

Shares of the struggling burger chain spiked 14% last Wednesday after noted investor Nelson Peltz made an offer to buy it. Shares rose more than 2% Thursday as the company reported a better than expected performance during the third quarter.

The company said Wednesday that a committee of independent directors unanimously rejected the offer because it “substantially undervalues” the company.

Wendy's also announced that it has adopted a shareholder's rights plan, a so-called “poison pill,” intended to avert a hostile takeover of the company. The plan, which grants all shareholders except the hostile bidder the right to purchase discounted shares, automatically triggers if a person or group owns 15% or more of Wendy's shares.

Peltz's Trian Fund Management and other partners in the investor group that made the offer to Wendy's hold 16.3% of the company's shares. The plan would stay in place for one year, Wendy's said.

Wendy's has wrestled with inflation like other fast food chains and lower-income customers have cut down on visits as the company raised prices to combat rising labor, food and packaging costs.