diff --git a/demo2.cpp b/demo2.cpp
index b4053d5..8f15cf9 100644
--- a/demo2.cpp
+++ b/demo2.cpp
@@ -774,6 +774,12 @@ Unit floorHeightAt(int16_t x, int16_t y)
   return UNITS_PER_SQUARE * 2;
 }
 
+Unit collisionAt(int16_t x, int16_t y)
+{
+  Unit square = level[(LEVEL_Y_RES - y -1) * LEVEL_X_RES + x];
+  return square == 0 || square == 6 ? 0 : UNITS_PER_SQUARE;
+}
+
 Unit textureAt(int16_t x, int16_t y)
 {
   Unit t = 0;
@@ -963,7 +969,7 @@ int main()
       }
 
       player.update(moveDirection,strafe,rotationDirection,false,0,
-        floorHeightAt,0,false,dt);
+        collisionAt,0,false,dt);
     }
   }