diff --git a/simple-pathfinding/src/main/java/fr/uha/gasser/pathfinding/algorithm/AStarSearch.java b/simple-pathfinding/src/main/java/fr/uha/gasser/pathfinding/algorithm/AStarSearch.java
index 28a31f7..571c034 100644
--- a/simple-pathfinding/src/main/java/fr/uha/gasser/pathfinding/algorithm/AStarSearch.java
+++ b/simple-pathfinding/src/main/java/fr/uha/gasser/pathfinding/algorithm/AStarSearch.java
@@ -69,7 +69,7 @@ class AStarSearch {
             // If the node is a wall, don't add it to the list
             if (grid.get(loc).isWall()) continue;
             // Don't overflow off the grid
-            if (loc.x > gridSize.width || loc.y > gridSize.height) continue;
+            if (loc.x >= gridSize.width || loc.y >= gridSize.height || loc.x < 0 || loc.y < 0) continue;
             node.setLoc(loc);
             neighbors.add(node);
         }
diff --git a/simple-pathfinding/src/main/java/fr/uha/gasser/pathfinding/ui/App.java b/simple-pathfinding/src/main/java/fr/uha/gasser/pathfinding/ui/App.java
index 3083003..23d31ac 100644
--- a/simple-pathfinding/src/main/java/fr/uha/gasser/pathfinding/ui/App.java
+++ b/simple-pathfinding/src/main/java/fr/uha/gasser/pathfinding/ui/App.java
@@ -29,6 +29,7 @@ public class App extends JFrame {
     private App() throws HeadlessException {
         super("Pathfinding");
         grid = new Grid(ROWS, COLS, CELL_SIZE);
+        generateWalls();
         setupInterface();
         pack();
         setVisible(true);
@@ -77,6 +78,16 @@ public class App extends JFrame {
         getContentPane().add(gridPane);
     }
 
+    /**
+     * Generate walls randomly at runtime
+     */
+    private void generateWalls() {
+        for (Cell cell : grid) {
+            final double wallProb = (Math.random() * ((0 - 0.2) + 1));
+            if (Math.random() < wallProb) grid.setWall(cell.getPos(), true);
+        }
+    }
+
     private void setWallPlacing(JMenuItem placeWallItem) {
         // Invert selection state
         placeWallItem.setSelected(!placeWallItem.isSelected());
@@ -100,6 +111,7 @@ public class App extends JFrame {
         startNode = null;
         endNode = null;
         grid.clear();
+        generateWalls();
     }
 
     private void doCancel() {