diff --git a/src/sim.c b/src/sim.c
index 3bebb15f..d68c622f 100644
--- a/src/sim.c
+++ b/src/sim.c
@@ -561,26 +561,18 @@ struct v2 sim_pos_from_world_tile_index(struct v2i32 world_tile_index)
     f32 tile_size = 1.f / SIM_TILES_PER_UNIT_SQRT;
     res.x = (f32)world_tile_index.x * tile_size;
     res.y = (f32)world_tile_index.y * tile_size;
-    if (world_tile_index.x < 0) {
-        res.x += tile_size;
-    }
-    if (world_tile_index.y < 0) {
-        res.y += tile_size;
-    }
     return res;
 }
 
 struct v2i32 sim_local_tile_index_from_world_tile_index(struct v2i32 world_tile_index)
 {
-    struct v2i32 res = ZI;
-    res.x = world_tile_index.x % SIM_TILES_PER_CHUNK_SQRT;
-    res.y = world_tile_index.y % SIM_TILES_PER_CHUNK_SQRT;
-    if (world_tile_index.x < 0) {
-        res.x = SIM_TILES_PER_CHUNK_SQRT + res.x - 1;
-    }
-    if (world_tile_index.y < 0) {
-        res.y = SIM_TILES_PER_CHUNK_SQRT + res.y - 1;
-    }
+    struct v2i32 res = world_tile_index;
+    res.x += res.x < 0;
+    res.y += res.y < 0;
+    res.x = res.x % SIM_TILES_PER_CHUNK_SQRT;
+    res.y = res.y % SIM_TILES_PER_CHUNK_SQRT;
+    res.x += (world_tile_index.x < 0) * (SIM_TILES_PER_CHUNK_SQRT - 1);
+    res.y += (world_tile_index.y < 0) * (SIM_TILES_PER_CHUNK_SQRT - 1);
     return res;
 }
 
@@ -594,9 +586,11 @@ struct v2i32 sim_world_tile_index_from_local_tile_index(struct v2i32 tile_chunk_
 
 struct v2i32 sim_tile_chunk_index_from_world_tile_index(struct v2i32 world_tile_index)
 {
-    struct v2i32 res = ZI;
-    res.x = world_tile_index.x / SIM_TILES_PER_CHUNK_SQRT;
-    res.y = world_tile_index.y / SIM_TILES_PER_CHUNK_SQRT;
+    struct v2i32 res = world_tile_index;
+    res.x += res.x < 0;
+    res.y += res.y < 0;
+    res.x = res.x / SIM_TILES_PER_CHUNK_SQRT;
+    res.y = res.y / SIM_TILES_PER_CHUNK_SQRT;
     res.x -= world_tile_index.x < 0;
     res.y -= world_tile_index.y < 0;
     return res;
diff --git a/src/sim_ent.c b/src/sim_ent.c
index f4172c4a..28c78bb3 100644
--- a/src/sim_ent.c
+++ b/src/sim_ent.c
@@ -566,11 +566,17 @@ void sim_ent_apply_torque(struct sim_ent *ent, f32 torque)
  * Tile
  * ========================== */
 
+struct sim_ent *sim_tile_chunk_from_chunk_index(struct sim_snapshot *ss, struct v2i32 chunk_index)
+{
+    struct sim_ent_id chunk_id = sim_ent_tile_chunk_id_from_tile_chunk_index(chunk_index);
+    struct sim_ent *chunk_ent = sim_ent_from_id(ss, chunk_id);
+    return chunk_ent;
+}
+
 struct sim_ent *sim_tile_chunk_from_world_tile_index(struct sim_snapshot *ss, struct v2i32 world_tile_index)
 {
     struct v2i32 chunk_index = sim_tile_chunk_index_from_world_tile_index(world_tile_index);
-    struct sim_ent_id chunk_id = sim_ent_tile_chunk_id_from_tile_chunk_index(chunk_index);
-    struct sim_ent *chunk_ent = sim_ent_from_id(ss, chunk_id);
+    struct sim_ent *chunk_ent = sim_tile_chunk_from_chunk_index(ss, chunk_index);
     return chunk_ent;
 }
 
diff --git a/src/sim_ent.h b/src/sim_ent.h
index aeef2597..00f91031 100644
--- a/src/sim_ent.h
+++ b/src/sim_ent.h
@@ -543,6 +543,7 @@ void sim_ent_apply_angular_impulse(struct sim_ent *ent, f32 impulse);
 void sim_ent_apply_torque(struct sim_ent *ent, f32 torque);
 
 /* Tile */
+struct sim_ent *sim_tile_chunk_from_chunk_index(struct sim_snapshot *ss, struct v2i32 chunk_index);
 struct sim_ent *sim_tile_chunk_from_world_tile_index(struct sim_snapshot *ss, struct v2i32 world_tile_index);
 enum sim_tile_kind sim_get_chunk_tile(struct sim_ent *chunk_ent, struct v2i32 local_tile_index);
 
diff --git a/src/sim_step.c b/src/sim_step.c
index 90555a25..ae0525df 100644
--- a/src/sim_step.c
+++ b/src/sim_step.c
@@ -429,8 +429,8 @@ INTERNAL void test_generate_walls(struct sim_ent *parent)
         if (!chunk->valid) continue;
         if (sim_ent_has_prop(chunk, SEPROP_TILE_CHUNK)) {
             struct v2i32 chunk_index = chunk->tile_chunk_index;
-            struct sim_ent *top_chunk = sim_tile_chunk_from_world_tile_index(world, V2I32(chunk_index.x, chunk_index.y - 1));
-            struct sim_ent *bottom_chunk = sim_tile_chunk_from_world_tile_index(world, V2I32(chunk_index.x, chunk_index.y + 1));
+            struct sim_ent *top_chunk = sim_tile_chunk_from_chunk_index(world, V2I32(chunk_index.x, chunk_index.y - 1));
+            struct sim_ent *bottom_chunk = sim_tile_chunk_from_chunk_index(world, V2I32(chunk_index.x, chunk_index.y + 1));
             /* If there's no chunk below this one, then do an extra iteration (since walls are created at the top of each tile) */
             i32 y_iterations = SIM_TILES_PER_CHUNK_SQRT + !bottom_chunk->valid;
             i32 x_iterations = SIM_TILES_PER_CHUNK_SQRT + 1;
@@ -439,20 +439,29 @@ INTERNAL void test_generate_walls(struct sim_ent *parent)
                 i32 wall_end = -1;
                 for (i32 tile_x = 0; tile_x < x_iterations; ++tile_x) {
                     enum sim_tile_kind tile = SIM_TILE_KIND_NONE;
-                    enum sim_tile_kind top_tile = SIM_TILE_KIND_NONE;
                     if (tile_x < SIM_TILES_PER_CHUNK_SQRT && tile_y < SIM_TILES_PER_CHUNK_SQRT) {
                         tile = sim_get_chunk_tile(chunk, V2I32(tile_x, tile_y));
                     }
-                    if (tile == SIM_TILE_KIND_NONE && tile_x < SIM_TILES_PER_CHUNK_SQRT) {
+                    b32 should_have_top_wall = false;
+                    if (tile_x < SIM_TILES_PER_CHUNK_SQRT) {
+                        enum sim_tile_kind top_tile = SIM_TILE_KIND_NONE;
                         if (tile_y == 0) {
                             if (top_chunk->valid) {
-                                top_tile = sim_get_chunk_tile(top_chunk, V2I32(tile_x, SIM_TILES_PER_CHUNK_SQRT - 1));
+                                struct v2i32 top_tile_local_index = V2I32(tile_x, SIM_TILES_PER_CHUNK_SQRT - 1);
+                                top_tile = sim_get_chunk_tile(top_chunk, top_tile_local_index);
                             }
                         } else {
                             top_tile = sim_get_chunk_tile(chunk, V2I32(tile_x, tile_y - 1));
                         }
+                        if (tile == SIM_TILE_KIND_WALL) {
+                            /* Process wall tile */
+                            should_have_top_wall = top_tile != SIM_TILE_KIND_WALL;
+                        } else {
+                            /* Process non-wall tile */
+                            should_have_top_wall = top_tile == SIM_TILE_KIND_WALL;
+                        }
                     }
-                    if (top_tile == SIM_TILE_KIND_WALL && tile != SIM_TILE_KIND_WALL) {
+                    if (should_have_top_wall) {
                         if (wall_start < 0) {
                             /* Start wall */
                             wall_start = tile_x;