diff --git a/src/hexyz.lua b/src/hexyz.lua
index 122e658..dc5539f 100644
--- a/src/hexyz.lua
+++ b/src/hexyz.lua
@@ -517,7 +517,7 @@ end
 --  function (from, to)         -- from and to are vec2's
 --      return some numeric value
 --
-function hex_Astar(map, start, goal, heuristic, cost_f)
+function hex_Astar(map, start, goal, cost_f, neighbour_f, heuristic)
     local path = {}
     hex_map_set(path, start, false)
 
@@ -536,7 +536,7 @@ function hex_Astar(map, start, goal, heuristic, cost_f)
             break
         end
 
-        for _,next_ in pairs(map.neighbours(current.hex)) do
+        for _,next_ in pairs(neighbour_f(map, current.hex)) do
             local new_cost = hex_map_get(path_so_far, current.hex.x, current.hex.y) + cost_f(map, current.hex, next_)
             local next_cost = hex_map_get(path_so_far, next_.x, next_.y)
 
diff --git a/src/mob.lua b/src/mob.lua
index c41c3d3..76ddc0a 100644
--- a/src/mob.lua
+++ b/src/mob.lua
@@ -120,10 +120,6 @@ function make_mob_node(mob_type, mob)
     end
 end
 
-function get_mob_path(mob, map, start, goal)
-    return Astar(map, goal, start, grid_heuristic, grid_cost)
-end
-
 local function get_spawn_hex()
     -- ensure we spawn on an random tile along the map's edges
     local roll = math.random(HEX_GRID_WIDTH * 2 + HEX_GRID_HEIGHT * 2) - 1
diff --git a/src/tower.lua b/src/tower.lua
index cea96dd..769d5a5 100644
--- a/src/tower.lua
+++ b/src/tower.lua
@@ -441,7 +441,7 @@ function update_tower_lighthouse(tower, tower_index)
                 -- is within some angle range...? if the mob is heading directly away from the tower, then
                 -- the lighthouse shouldn't do much
 
-                local path, made_it = hex_Astar(state.map, tower.hex, m.hex, grid_heuristic, grid_cost)
+                local path, made_it = hex_Astar(state.map, tower.hex, m.hex, grid_neighbours, grid_cost, heuristic)
 
                 if made_it then
                     m.path = path