Gather the ingredients.

Place cherries into a saucepan over medium heat. Cover and cook, stirring often, until cherries release their juices and come to a simmer, 10 to 15 minutes.

Whisk sugar with cornstarch in a bowl until combined; pour mixture into hot cherries and juice. Stir until thoroughly combined.

Bring to a simmer over low heat; cook until thickened, about 2 minutes. Remove from heat and let cool before using as pie filling.