diff --git a/lib/Board.cpp b/lib/Board.cpp
index db04da9..0de0e91 100644
--- a/lib/Board.cpp
+++ b/lib/Board.cpp
@@ -54,7 +54,7 @@ constexpr std::array<std::array<int, COLUMNS>, ROWS> board = {{
 // clang-format on
 
 static Cell cellAtPosition(GridPosition point) {
-  if (point.x >= COLUMNS || point.y >= ROWS)
+  if (point.x < 0 || point.x >= COLUMNS || point.y < 0 || point.y >= ROWS)
     return Cell::wall;
   return Cell(board[point.y][point.x]);
 }
@@ -64,10 +64,10 @@ bool isWalkableForPacMan(GridPosition point) {
 }
 
 bool isWalkableForGhost(GridPosition point, GridPosition origin, bool isEyes) {
-  Cell cell = cellAtPosition(point);
+  const Cell cell = cellAtPosition(point);
   if (cell == Cell::wall)
     return false;
-  return isEyes || (isInPen(origin) || !isInPen(point));
+  return isEyes || isInPen(origin) || !isInPen(point);
 }
 
 bool isInPen(GridPosition point) {
diff --git a/lib/Ghost.cpp b/lib/Ghost.cpp
index 4dfaf59..68f4eec 100644
--- a/lib/Ghost.cpp
+++ b/lib/Ghost.cpp
@@ -95,6 +95,9 @@ void Ghost::updatePosition(std::chrono::milliseconds time_delta, const GameState
 
   double position_delta = (0.004 * time_delta.count()) * speed(gameState);
 
+  const auto old_position = pos;
+  const GridPosition old_grid_position = positionToGridPosition(old_position);
+
   switch (direction) {
     case Direction::NONE:
       break;
@@ -119,6 +122,10 @@ void Ghost::updatePosition(std::chrono::milliseconds time_delta, const GameState
   if (isPortal(positionInGrid(), direction)) {
     pos = gridPositionToPosition(teleport(positionInGrid()));
   }
+  else if (!isWalkableForGhost(positionInGrid(), old_grid_position, isEyes())) {
+    pos = old_position;
+    direction = oppositeDirection(direction);
+  }
 }
 
 /*
@@ -160,7 +167,6 @@ void Ghost::updateDirection(const GameState & gameState) {
   const Position target_position = target(gameState);
 
   for (auto & move : possible_moves) {
-
     if (isPortal(current_grid_position, move.direction))
       move.position = gridPositionToPosition(teleport(current_grid_position));
 
@@ -172,7 +178,7 @@ void Ghost::updateDirection(const GameState & gameState) {
     if (opposite_direction)
       continue;
 
-    const GridPosition grid_position = { size_t(move.position.x), size_t(move.position.y) };
+    const GridPosition grid_position = { int64_t(move.position.x), int64_t(move.position.y) };
     const bool can_walk = isWalkableForGhost(grid_position, current_grid_position, isEyes());
     if (!can_walk)
       continue;
@@ -184,7 +190,7 @@ void Ghost::updateDirection(const GameState & gameState) {
     return a.distance_to_target < b.distance_to_target;
   });
 
-  const auto& move = *optimal_move;
+  const auto & move = *optimal_move;
   direction = move.direction;
   last_grid_position = current_grid_position;
 }
diff --git a/lib/Inky.cpp b/lib/Inky.cpp
index 6b258ac..ab8d268 100644
--- a/lib/Inky.cpp
+++ b/lib/Inky.cpp
@@ -53,8 +53,8 @@ Position Inky::target(const GameState & gameState) const {
 
   // And selects a point on the line crossing blinky and this position that is at twice that distance
   // away from blinky
-  targetPosition.x += size_t((targetPosition.x - blinkyPosition.x) / distanceBetweenBlinkyAndTarget) * 2;
-  targetPosition.y += size_t((targetPosition.y - blinkyPosition.y) / distanceBetweenBlinkyAndTarget) * 2;
+  targetPosition.x += int64_t((targetPosition.x - blinkyPosition.x) / distanceBetweenBlinkyAndTarget) * 2;
+  targetPosition.y += int64_t((targetPosition.y - blinkyPosition.y) / distanceBetweenBlinkyAndTarget) * 2;
 
   return gridPositionToPosition(targetPosition);
 }
diff --git a/lib/PacMan.cpp b/lib/PacMan.cpp
index 25d1b89..a78ea5f 100644
--- a/lib/PacMan.cpp
+++ b/lib/PacMan.cpp
@@ -64,13 +64,13 @@ void PacMan::updateMazePosition(std::chrono::milliseconds time_delta) {
   auto moveToPosition = [position_delta](Position point, Direction move_direction) {
     switch (move_direction) {
       case Direction::LEFT:
-        return GridPosition{ std::size_t(point.x - position_delta), std::size_t(point.y) };
+        return GridPosition{ int64_t(point.x - position_delta), int64_t(point.y) };
       case Direction::RIGHT:
-        return GridPosition{ std::size_t(point.x + pacman_size), std::size_t(point.y) };
+        return GridPosition{ int64_t(point.x + pacman_size), int64_t(point.y) };
       case Direction::UP:
-        return GridPosition{ std::size_t(point.x), std::size_t(point.y - position_delta) };
+        return GridPosition{ int64_t(point.x), int64_t(point.y - position_delta) };
       case Direction::DOWN:
-        return GridPosition{ std::size_t(point.x), std::size_t(point.y + pacman_size) };
+        return GridPosition{ int64_t(point.x), int64_t(point.y + pacman_size) };
       case Direction::NONE:
       default:
         return positionToGridPosition(point);
diff --git a/lib/PacManAnimation.cpp b/lib/PacManAnimation.cpp
index ea67a25..37e2b5e 100644
--- a/lib/PacManAnimation.cpp
+++ b/lib/PacManAnimation.cpp
@@ -32,15 +32,13 @@ void PacManAnimation::updateAnimationPosition(std::chrono::milliseconds time_del
     return;
 
   animation_position_delta += (0.02) * double(time_delta.count());
-
-  animation_position = int(animation_position + animation_position_delta);
+  animation_position = int64_t(animation_position + animation_position_delta);
 
   if (!dead)
       animation_position = animation_position % 4;
 
   if(animation_position_delta > 1)
       animation_position_delta = animation_position_delta - 1;
-
 }
 
 void PacManAnimation::pause() {
diff --git a/lib/include/Atlas.hpp b/lib/include/Atlas.hpp
index 530d885..d5226f3 100644
--- a/lib/include/Atlas.hpp
+++ b/lib/include/Atlas.hpp
@@ -47,8 +47,8 @@ constexpr GridPosition eyeSprite(Direction direction) {
 
 constexpr GridPosition ghostSprite(Ghost ghost, Direction direction, bool alternative) {
   assert(ghost >= Ghost::blinky && ghost <= Ghost::clyde && "Invalid Ghost");
-  auto y = static_cast<size_t>(ghost);
-  size_t x = 0;
+  auto y = static_cast<int64_t>(ghost);
+  int64_t x = 0;
   switch (direction) {
     case Direction::RIGHT:
       x = 0;
diff --git a/lib/include/Board.hpp b/lib/include/Board.hpp
index fe30302..d3fc6ec 100644
--- a/lib/include/Board.hpp
+++ b/lib/include/Board.hpp
@@ -18,8 +18,7 @@ std::vector<GridPosition> initialPelletPositions();
 
 std::vector<GridPosition> initialSuperPelletPositions();
 
-inline Position penDoorPosition() {
-  return { 13, 11 }; }
-  inline Position initialPacManPosition() { return { 13.5, 23 }; }
+inline Position penDoorPosition() { return { 13, 11 }; }
+inline Position initialPacManPosition() { return { 13.5, 23 }; }
 
-  } // namespace pacman
+} // namespace pacman
diff --git a/lib/include/PacManAnimation.hpp b/lib/include/PacManAnimation.hpp
index 42dcde0..4c4e520 100644
--- a/lib/include/PacManAnimation.hpp
+++ b/lib/include/PacManAnimation.hpp
@@ -18,7 +18,7 @@ public:
   void pause();
 
 private:
-  size_t animation_position = 0;
+  int64_t animation_position = 0;
   double animation_position_delta = 0.0;
 };
 
diff --git a/lib/include/Position.hpp b/lib/include/Position.hpp
index a3f1a97..40eb798 100644
--- a/lib/include/Position.hpp
+++ b/lib/include/Position.hpp
@@ -10,13 +10,13 @@ struct Position {
 };
 
 struct GridPosition {
-  size_t x;
-  size_t y;
-  constexpr GridPosition(size_t x, size_t y) : x(x), y(y) {}
+  int64_t x;
+  int64_t y;
+  constexpr GridPosition(int64_t x, int64_t y) : x(x), y(y) {}
 };
 
 inline GridPosition positionToGridPosition(Position pos) {
-  return { size_t(std::round(pos.x)), size_t(std::round(pos.y)) };
+  return { int64_t(std::round(pos.x)), int64_t(std::round(pos.y)) };
 }
 
 inline Position gridPositionToPosition(GridPosition pos) {