Hertz Global Holdings Inc. shares had their biggest gain ever after CNBC reported that Pershing Square Capital Management had amassed a position of almost 20% in the beleaguered car rental company.

Bill Ackman’s investment firm said in a filing Wednesday that it bought 12.7 million shares valued at about $46.5 million at the time of the purchase. CNBC’s Scott Wapner later reported that the position was about 19.8% including shares and swaps, making Pershing Square the company’s second-largest shareholder.

Hertz shares jumped 56% at the close of New York trading and continued to gain in the postmarket session.

The stock had fallen 47% over the prior 12 months. Hertz has been working to revamp its fleet and position the company for growth following an ill-advised bet on Tesla Inc. electric vehicles, which were unpopular with customers and expensive to maintain. Hertz emerged from bankruptcy in 2021.

Representatives for Pershing Square and Hertz didn’t immediately respond to requests seeking comment.