Mentor isn’t going to let Carl Icahn break up the company without a fight.

That’s my take, given the EDA software company’s latest maneuver. Mentor has adopted something called a “Shareholder Rights Plan,” in which it will grant each of its shareholders the opportunity to purchase one discounted share for each share of common stock currently held. This option to buy kicks in if a person, alone or as part of a group effort, accumulates 15% or more of Mentor stock (or announces an offer to do so).

The move “enables the board to protect the company and to allow all of the shareholders to realize the long-term value of their investment,” the firm said in a press release.

This is a variation of the traditional poison pill defense some companies take when they are perceived to be in play by unwanted investors. The idea is to either slow down the third party, giving the board time to find a more desirable buyer, or to make it so expensive to acquire a controlling stake in the company, the third party will give up.

I, for one, am glad to see Mentor taking this step.