Lionsgate’s stock price is down more than 2.9% in post-market trading after it announced the secondary offering that will reduce Chairman Mark Rachesky’s stake in the studio to about 28% from 35%.

His investment firm, MHR Fund Management, will offer 10 million shares, and give underwriter J.P. Morgan Securities an option to buy an additional 1.5 million.Lionsgate has about 145.5 million shares outstanding; MHR currently has 51.3 million of the total. The stock closed today at $33.68 a share.

None of the cash from the offering will go to Lionsgate. Rachesky could use it to start a new investment fund. Underwriters will decide later what price they will set on the offering. It’s as good a time as any to sell. Lionsgate’s stock price rose 25.7% over the last 12 months.

Rachesky’s decision to offer a portion of his holdings to the public may slightly dampen speculation that he might sell his controlling stake to a company such as China’s Alibaba or Wanda Group that wants a foothold in Hollywood.

But when an insider sells a big chunk of stock, some investors inevitably wonder whether it’s a sign that the company’s prospects are shakier than management lets on. Last week CEO Jon Feltheimer disclosed in an SEC filing that he sold 250,000 shares valued at $8.4 million. It was part of an ongoing stock sale plan that began in September, designed to sell 1 million shares over a one-year period.