Index: /applications/editors/josm/plugins/terracer/src/terracer/TerracerAction.java
===================================================================
--- /applications/editors/josm/plugins/terracer/src/terracer/TerracerAction.java	(revision 14047)
+++ /applications/editors/josm/plugins/terracer/src/terracer/TerracerAction.java	(revision 14048)
@@ -321,9 +321,10 @@
 
 	/**
-	 * Calculate the length of a side (from node i to i+1) in a way.
+	 * Calculate the length of a side (from node i to i+1) in a way. This assumes that
+	 * the way is closed, but I only ever call it for buildings.
 	 */
 	private double sideLength(Way w, int i) {
 		Node a = w.nodes.get(i);
-		Node b = w.nodes.get(i+1);
+		Node b = w.nodes.get((i+1) % (w.nodes.size() - 1));
 		return a.coor.greatCircleDistance(b.coor);
 	}
@@ -369,5 +370,5 @@
 
 	/**
-	 * Calculate "sideness" metric for each segment in a way.
+	 * Calculate "sideness" metric for each segment in a way.  
 	 */
 	private double[] calculateSideness(Way w) {