Preheat oven to 425 degrees.
Combine flour, 1/2 cup sugar, cinnamon and blueberries. Mix well and put into pie shell. Drizzle top with lemon juice.
Combine 1/2 cup brown sugar and flour. Cut in butter until mixture resembles coarse meal. Spread topping over berries.
Bake for 30 minutes at 425 degrees, then cover with foil and continue baking for 20 minutes more.