diff --git a/main.lua b/main.lua
index 1e4f466..8fcb375 100644
--- a/main.lua
+++ b/main.lua
@@ -177,13 +177,9 @@ local function move_bubble(x, y, velocity_x, velocity_y)
   }
 end
 
-local function generate_aim_guide(towards_x, towards_y)
-  -- TODO: don't allow aiming backwards
-  local diff_x = towards_x - game.launcher_x
-  local diff_y = towards_y - game.launcher_y
-  local dist = math.sqrt(diff_x * diff_x + diff_y * diff_y)
-  local velocity_x = diff_x / dist * game.bubble_speed
-  local velocity_y = diff_y / dist * game.bubble_speed
+local function generate_aim_guide(angle)
+  local velocity_x = math.cos(angle) * game.bubble_speed
+  local velocity_y = math.sin(angle) * game.bubble_speed
   local new_x = game.launcher_x
   local new_y = game.launcher_y
   local radius = 5
@@ -354,7 +350,7 @@ local function start_level()
 
   game.show_aim_guide = true
   game.aim_guide = {}
-  generate_aim_guide(game.window_width / 2, game.window_height / 2)
+  generate_aim_guide(game.launcher_rotation)
 
   game.bursting_bubbles = {}
   game.falling_bubbles = {}
@@ -527,7 +523,7 @@ function love.update(dt)
       game.ceiling_drop_tween = nil
     end
     if game.show_aim_guide then
-      generate_aim_guide(love.mouse:getX(), love.mouse:getY())
+      generate_aim_guide(game.launcher_rotation)
     end
   end
 
@@ -632,7 +628,7 @@ function love.update(dt)
       end
 
       if game.show_aim_guide then
-        generate_aim_guide(love.mouse:getX(), love.mouse:getY())
+        generate_aim_guide(game.launcher_rotation)
       end
 
       -- calculate remaining bubble types
@@ -952,13 +948,13 @@ function love.mousepressed(x, y, button, is_touch, presses)
      game.current_bubble.y == game.launcher_y and
      game.current_bubble.velocity_x == 0 and
      game.current_bubble.velocity_y == 0 then
-    local diff_x = x - game.launcher_x
-    local diff_y = y - game.launcher_y
-    local dist = math.sqrt(diff_x * diff_x + diff_y * diff_y)
-    -- TODO: don't allow shooting backwards
 
-    game.current_bubble.velocity_x = diff_x / dist * game.bubble_speed
-    game.current_bubble.velocity_y = diff_y / dist * game.bubble_speed
+    -- use the angle from mousemoved to calculate the velocity so that shooting
+    -- backwards is not possible
+    game.current_bubble.velocity_x =
+      math.cos(game.launcher_rotation) * game.bubble_speed
+    game.current_bubble.velocity_y =
+      math.sin(game.launcher_rotation) * game.bubble_speed
 
     game.bubbles_launched = game.bubbles_launched + 1
 
@@ -973,13 +969,24 @@ function love.mousemoved(x, y, dx, dy, is_touch)
   if not game.game_over then
     local diff_x = x - game.launcher_x
     local diff_y = y - game.launcher_y
-    local rotation = math.atan2(diff_y, diff_x)
-    if rotation >= -tau * 7 / 16 and rotation <= -tau / 16 then
-      game.launcher_rotation = rotation
+    local angle = math.atan2(diff_y, diff_x)
+
+    -- force angle to be positive
+    if y < game.launcher_y then
+      angle = angle + tau
     end
 
+    -- don't allow aiming backwards
+    if (angle >= 0 and angle <= tau / 4) or angle >= tau * 25 / 26 then
+      angle = tau * 25 / 26
+    elseif angle >= tau / 4 and angle <= tau * 14 / 26 then
+      angle = tau * 14 / 26
+    end
+
+    game.launcher_rotation = angle
+
     if game.show_aim_guide then
-      generate_aim_guide(x, y)
+      generate_aim_guide(game.launcher_rotation)
     end
   end
 end