Preheat oven to 375 degrees.
Butter a 9x13 inch baking dish and set aside.
Combine the flour, sugar, and cinnamon in a bowl.
Blend in the butter with a pastry cutter or your fingers until the mixture is crumbly.
Place the blueberries in the prepared baking dish and sprinkle the crumb mixture over them.
Bake 30 to 35 minutes.
Serve with vanilla ice cream, if desired.