Preheat the oven to 350 degrees F (175 degrees C).
Place the blueberries into an 8” square-baking dish.
In a medium bowl, stir together the flour, sugar, and cinnamon. Stir in the mayonnaise until the mixture resembles coarse crumbs. Sprinkle over the top of the berries.
Bake for 35 to 40 minutes in the preheated oven, until the top is lightly browned.