Preheat oven to 350°F (175°C) and grease a 9x13 inch baking dish.

Spread the blueberries evenly in the bottom of the prepared dish and sprinkle with granulated sugar.

Sprinkle the dry cake mix evenly over the blueberry layer.

Pour the melted butter uniformly over the top of the cake mix, ensuring as much area is covered as possible.

Bake for 40 minutes, or until the topping is golden brown and the fruit is bubbling.