diff --git a/contents/2_Q_Learning_maze/maze_env.py b/contents/2_Q_Learning_maze/maze_env.py
index d54b51f..1d69ada 100644
--- a/contents/2_Q_Learning_maze/maze_env.py
+++ b/contents/2_Q_Learning_maze/maze_env.py
@@ -42,7 +42,7 @@ def _build_maze(self):
 
         # create grids
         for c in range(0, MAZE_W * UNIT, UNIT):
-            x0, y0, x1, y1 = c, 0, c, MAZE_H * UNIT
+            x0, y0, x1, y1 = c, 0, c, MAZE_W * UNIT
             self.canvas.create_line(x0, y0, x1, y1)
         for r in range(0, MAZE_H * UNIT, UNIT):
             x0, y0, x1, y1 = 0, r, MAZE_H * UNIT, r