diff --git a/src/micropolisj/gui/OverlayMapView.java b/src/micropolisj/gui/OverlayMapView.java
index 9e21b4f..c6c6b42 100644
--- a/src/micropolisj/gui/OverlayMapView.java
+++ b/src/micropolisj/gui/OverlayMapView.java
@@ -325,7 +325,11 @@ public class OverlayMapView extends JComponent
 				default:
 				}
 
+				// tile == -1 means it's already been drawn
+				// in the checkPower function
+
 				if (tile != -1) {
+				if (tile >= 0 && tile <= LAST_TILE) {
 				for (int yy = 0; yy < TILE_HEIGHT; yy++)
 				{
 					for (int xx = 0; xx < TILE_WIDTH; xx++)
@@ -335,6 +339,7 @@ public class OverlayMapView extends JComponent
 					}
 				}
 				}
+				}
 			}
 		}