The demise of Toys R Us in the U.S. has left billions of dollars in sales up for grabs, and Party City Holdco Inc. is going after that gaping hole.

Party City plans to operate 50 pop-up toy stores from September through the holiday shopping season, possibly in former locations of the defunct chain, executives said in an interview. The assortment will include top brands from Hasbro and Mattel and plenty of Santa suits and stockings for Christmas.

Party City is also adding more toys to its website as part of a push into the category. If the pop-up pilot goes well, the company will likely expand the format next year.

“Customers are going to be looking for something to fill that void, and we intend to do that,” said Ryan Vero, Party City’s president of retail.

Since Toys R Us began liquidating its U.S. business earlier this year, there have been few signs that other major outlets would expand toy offerings.