A lot of players must have preordered Whispers of the Old Gods.

Acitvision Blizzard released its financial results for Q1 2016 today, a period that ended on March 31. That’s well before the release of the latest expansion, Whispers of the Old Gods, which came out on April 26. Still, non-GAAP revenues for the free-to-play game rose 20 percent compared to the previous quarter. Preorders (which allowed players to preroder 50 packs of cards for $50) were available during that time, so that may have driven growth. Whatever the reason, Hearthstone continues to dominate the $1.2 billion digital card game market with its over 50 million registered players.

Hearthstone was Blizzard’s first free-to-play game, and the experiment has definitely paid off. It’s become a reliable money-maker the Warcraft maker, which has since released another free-to-play title, the multiplayer online battle arena (MOBA) Heroes of the Storm.

The whole company is doing well thanks to a strong stable of games that includes those free-to-play titles and World of Warcraft, Diablo III, and StarCraft II. Combining all games, Blizzard had 26 million active monthly users during the first quarter, which was up 23 percent over the same period last year. The developer is also about to release a new premium game, the team-based shooter Overwatch, on PlayStation 4, Xbox One, and PC on May 24 (although it is currently in open beta).