diff --git a/js/id/geo/extent.js b/js/id/geo/extent.js
index 8548fbff4..2b3813293 100644
--- a/js/id/geo/extent.js
+++ b/js/id/geo/extent.js
@@ -11,7 +11,7 @@ iD.geo.Extent = function geoExtent(min, max) {
     }
 };
 
-iD.geo.Extent.prototype = [[], []];
+iD.geo.Extent.prototype = new Array(2);
 
 _.extend(iD.geo.Extent.prototype, {
     extend: function(obj) {