diff --git a/MoreInterestingDungeons/cellular/src/map_builder/automata.rs b/MoreInterestingDungeons/cellular/src/map_builder/automata.rs
index 1c21dac..d22ac70 100644
--- a/MoreInterestingDungeons/cellular/src/map_builder/automata.rs
+++ b/MoreInterestingDungeons/cellular/src/map_builder/automata.rs
@@ -16,6 +16,7 @@ impl MapArchitect for CellularAutomataArchitect {
         for _ in 0..10 {
             self.iteration(&mut mb.map);
         }
+        self.add_boundaries(&mut mb.map);
         let start = self.find_start(&mb.map);
         mb.monster_spawns = mb.spawn_monsters(&start, rng);
         mb.player_start = start;
@@ -71,6 +72,19 @@ impl CellularAutomataArchitect {
         map.tiles = new_tiles;
     }
 
+    fn add_boundaries(&mut self, map: &mut Map) {
+        for x in 1 .. SCREEN_WIDTH {
+            map.tiles[map_idx(x, 1)] = TileType::Wall;
+            map.tiles[map_idx(x, SCREEN_HEIGHT-1)] = TileType::Wall;
+            map.tiles[map_idx(x, 0)] = TileType::Wall;
+        }
+        for y in 1 .. SCREEN_HEIGHT {
+            map.tiles[map_idx(1, y)] = TileType::Wall;
+            map.tiles[map_idx(SCREEN_WIDTH-1, y)] = TileType::Wall;
+            map.tiles[map_idx(0, y)] = TileType::Wall;
+        }
+    }
+
     fn find_start(&self, map: &Map) -> Point {
         let center = Point::new(SCREEN_WIDTH/2, SCREEN_HEIGHT/2);// (10)
         let closest_point = map.tiles
diff --git a/MoreInterestingDungeons/output_harness/src/map_builder/automata.rs b/MoreInterestingDungeons/output_harness/src/map_builder/automata.rs
index c173606..794b0e5 100644
--- a/MoreInterestingDungeons/output_harness/src/map_builder/automata.rs
+++ b/MoreInterestingDungeons/output_harness/src/map_builder/automata.rs
@@ -85,10 +85,12 @@ impl CellularAutomataArchitect {
         for x in 1 .. SCREEN_WIDTH {
             self.map.tiles[map_idx(x, 1)] = TileType::Wall;
             self.map.tiles[map_idx(x, SCREEN_HEIGHT-1)] = TileType::Wall;
+            self.map.tiles[map_idx(x, 0)] = TileType::Wall;
         }
         for y in 1 .. SCREEN_HEIGHT {
             self.map.tiles[map_idx(1, y)] = TileType::Wall;
             self.map.tiles[map_idx(SCREEN_WIDTH-1, y)] = TileType::Wall;
+            self.map.tiles[map_idx(0, y)] = TileType::Wall;
         }
     }