Marie Callender’s and Hungry-Man are joining together in a deal intended to create a bigger player in the frozen food aisle.

Conagra said Wednesday it is buying Pinnacle Foods for about $10.9 billion, citing in part the potential to capitalize on the recent resurgence of frozen food sales. But investors were skeptical of the combination, and shares of both companies fell.

Conagra also owns the Banquet, Healthy Choice and Alexia frozen brands, while Pinnacle owns Birds Eye, Van de Kamp’s and Mrs. Paul’s. The companies also own other packaged food brands, such as Chef Boyardee, Reddi-Wip and Duncan Hines.

The deal comes amid optimism for supermarket freezer sections after years of disappointing sales. Kellogg reported a jump in frozen food sales earlier this year, citing more millennials focusing on healthier frozen food options. Conagra also said its frozen and refrigerated unit is seeing growth, and CEO Sean Connolly said the category is just starting to benefit from modernization.

But it’s not clear how far that growth can continue.

Dewey Warner, a research analyst with Euromonitor, said frozen food sales have improved in large part because manufacturers have finally invested in revamping “stale, processed, traditional TV dinners” to make them more on-trend with simpler ingredient lists that seem less processed and new flavors.

But Warner said the broader trend toward fresh foods might limit the long-term growth potential of the freezer brands. He noted that U.S. sales of frozen food meals last year were still below 2010 levels, even with the recent improvements.

The deal also marks the latest shift in the reconfiguration of the U.S. food industry. Big food makers are being pressured by smaller companies that often offer products marketed and seen by consumers as being healthier.

The difficulty large companies have had in increasing sales has prompted established food makers to find other ways to improve financial results. That includes slashing costs and combining to help merge manufacturing or other operations.

Conagra Brands Inc. said the deal is targeted to close by the end of the year. It still needs approval from Pinnacle shareholders.

Shareholders of Parsippany, New Jersey, based-Pinnacle will receive $43.11 per share in cash and 0.6494 shares of Conagra stock for each share of Pinnacle. The transaction also includes Pinnacle’s outstanding debt.

Pinnacle shareholders are expected to own about 16 percent of the combined company.