diff --git a/src/engine/map/mod.rs b/src/engine/map/mod.rs
index 7ff5c48..e12ec12 100644
--- a/src/engine/map/mod.rs
+++ b/src/engine/map/mod.rs
@@ -303,23 +303,23 @@ impl Map {
     }
 
     /// Creates the neighbours of a tile.
-    pub fn neighbours(&self, i: isize, j: isize) -> [Option<CollisionTile>; 8] {
+    pub fn neighbours(&self, i: usize, j: usize) -> [Option<CollisionTile>; 8] {
         [
-            self.collision_tiles.get_isize(i - 1, j - 1).cloned(),
-            self.collision_tiles.get_isize(i - 1, j    ).cloned(),
-            self.collision_tiles.get_isize(i - 1, j + 1).cloned(),
-            self.collision_tiles.get_isize(i    , j + 1).cloned(),
-            self.collision_tiles.get_isize(i + 1, j + 1).cloned(),
-            self.collision_tiles.get_isize(i + 1, j    ).cloned(),
-            self.collision_tiles.get_isize(i + 1, j - 1).cloned(),
-            self.collision_tiles.get_isize(i    , j - 1).cloned(),
+            if i > 0 && j > 0 { self.collision_tiles.get(i - 1, j - 1).cloned() } else { None },
+            if i > 0          { self.collision_tiles.get(i - 1, j    ).cloned() } else { None },
+            if i > 0          { self.collision_tiles.get(i - 1, j + 1).cloned() } else { None },
+                                self.collision_tiles.get(i    , j + 1).cloned(),
+                                self.collision_tiles.get(i + 1, j + 1).cloned(),
+                                self.collision_tiles.get(i + 1, j    ).cloned(),
+            if j > 0          { self.collision_tiles.get(i + 1, j - 1).cloned() } else { None },
+            if j > 0          { self.collision_tiles.get(i    , j - 1).cloned() } else { None },
         ]
     }
 
     /// Returns the graphic tile corresponding to the collision tiles.
     pub fn graphic_tile(&self, i: usize, j: usize) -> GraphicTile {
         if self.collision_tiles[(i, j)].is_full() {
-            GraphicTile::from_neighbour_options(&self.neighbours(i as isize, j as isize))
+            GraphicTile::from_neighbour_options(&self.neighbours(i, j))
         } else {
             GraphicTile(None)
         }
@@ -327,7 +327,7 @@ impl Map {
 
     /// Returns a tile of the map.
     pub fn collision_tile(&self, i: usize, j: usize) -> Option<CollisionTile> {
-        self.collision_tiles.get((i, j)).cloned()
+        self.collision_tiles.get(i, j).cloned()
     }
 
     /// Changes a tile of the map.
@@ -339,7 +339,7 @@ impl Map {
         for i in (i - 1) ..= (i + 1) {
             for j in (j - 1) ..= (j + 1) {
                 let new_tile = self.graphic_tile(i, j);
-                if let Some(tile) = self.graphic_tiles.get_mut((i, j)) {
+                if let Some(tile) = self.graphic_tiles.get_mut(i, j) {
                     *tile = new_tile;
                 }
             }
diff --git a/src/engine/math/mod.rs b/src/engine/math/mod.rs
index 837b375..087761f 100644
--- a/src/engine/math/mod.rs
+++ b/src/engine/math/mod.rs
@@ -70,7 +70,7 @@ impl<T> Matrix<T> {
     }
 
     /// Returns the tile if any, none otherwise.
-    pub fn get(&self, (row, col): (usize, usize)) -> Option<&T> {
+    pub fn get(&self, row: usize, col: usize) -> Option<&T> {
         if row < self.rows && col < self.cols {
             Some(&self[(row, col)])
         } else {
@@ -78,18 +78,8 @@ impl<T> Matrix<T> {
         }
     }
 
-
-    /// Returns the tile if any, none otherwise.
-    pub fn get_isize(&self, row: isize, col: isize) -> Option<&T> {
-        if row >= 0 && col >= 0 && (row as usize) < self.rows && (col as usize) < self.cols {
-            Some(&self[(row as usize, col as usize)])
-        } else {
-            None
-        }
-    }
-
     /// Returns a mutable reference to the tile if any.
-    pub fn get_mut(&mut self, (row, col): (usize, usize)) -> Option<&mut T> {
+    pub fn get_mut(&mut self, row: usize, col: usize) -> Option<&mut T> {
         if row < self.rows && col < self.cols {
             Some(&mut self[(row, col)])
         } else {