diff --git a/index.js b/index.js
index 4aba334..f663863 100644
--- a/index.js
+++ b/index.js
@@ -55,7 +55,7 @@ function polygonArea(coords) {
 function ringArea(coords) {
     var p1, p2, p3, lowerIndex, middleIndex, upperIndex, i,
     area = 0,
-    coordsLength = coords.length;
+    coordsLength = coords.length - 1;
 
     if (coordsLength > 2) {
         for (i = 0; i < coordsLength; i++) {
@@ -86,4 +86,4 @@ function ringArea(coords) {
 
 function rad(_) {
     return _ * Math.PI / 180;
-}
\ No newline at end of file
+}