diff --git a/src/micropolisj/engine/Micropolis.java b/src/micropolisj/engine/Micropolis.java
index eb5fbb0..2a6a109 100644
--- a/src/micropolisj/engine/Micropolis.java
+++ b/src/micropolisj/engine/Micropolis.java
@@ -1106,7 +1106,7 @@ public class Micropolis
 								continue;
 							}
 							plevel += getPollutionValue(tile);
-							if (tile >= ROADBASE)
+							if (isConstructed(tile))
 								lvflag++;
 						}
 					}
@@ -2342,7 +2342,7 @@ public class Micropolis
 					continue;
 
 				int t = getTile(xtem, ytem);
-				if ((t & LOMASK) >= ROADBASE) {
+				if (isConstructed(t)) {
 					setTile(xtem, ytem, (char)(t | BULLBIT));
 				}
 			}
diff --git a/src/micropolisj/engine/TileConstants.java b/src/micropolisj/engine/TileConstants.java
index be55503..728aa5c 100644
--- a/src/micropolisj/engine/TileConstants.java
+++ b/src/micropolisj/engine/TileConstants.java
@@ -408,6 +408,11 @@ public class TileConstants
 		}
 	}
 
+	public static boolean isConstructed(int tile)
+	{
+		return tile >= 0 && (tile & LOMASK) >= ROADBASE;
+	}
+
 	static boolean isRiverEdge(int tile)
 	{
 		return (tile & LOMASK) > 4 && (tile & LOMASK) < 21;