diff --git a/src/ol/base/coveragearea.js b/src/ol/base/coveragearea.js
index d925452f48..aea8c3a067 100644
--- a/src/ol/base/coveragearea.js
+++ b/src/ol/base/coveragearea.js
@@ -6,17 +6,16 @@ goog.require('ol.Extent');
 
 /**
  * @constructor
- * @extends {ol.Extent}
- * @param {number} minX Minimum X.
- * @param {number} minY Minimum Y.
- * @param {number} maxX Maximum X.
- * @param {number} maxY Maximum Y.
+ * @param {ol.Extent} extent Extent.
  * @param {number} minZ Minimum Z.
  * @param {number} maxZ Maximum Z.
  */
-ol.CoverageArea = function(minX, minY, maxX, maxY, minZ, maxZ) {
+ol.CoverageArea = function(extent, minZ, maxZ) {
 
-  goog.base(this, minX, minY, maxX, maxY);
+  /**
+   * @type {ol.Extent}
+   */
+  this.extent = extent;
 
   /**
    * @type {number}
@@ -29,7 +28,6 @@ ol.CoverageArea = function(minX, minY, maxX, maxY, minZ, maxZ) {
   this.maxZ = maxZ;
 
 };
-goog.inherits(ol.CoverageArea, ol.Extent);
 
 
 /**
@@ -38,17 +36,15 @@ goog.inherits(ol.CoverageArea, ol.Extent);
  * @return {boolean} Intersects.
  */
 ol.CoverageArea.prototype.intersectsWithZ = function(extent, z) {
-  return this.intersects(extent) && this.minZ <= z && z <= this.maxZ;
+  return this.extent.intersects(extent) && this.minZ <= z && z <= this.maxZ;
 };
 
 
 /**
- * @override
  * @param {ol.TransformFunction} transformFn Transform.
  * @return {ol.CoverageArea} Transformed coverage area.
  */
 ol.CoverageArea.prototype.transform = function(transformFn) {
-  var min = transformFn(new ol.Coordinate(this.minX, this.minY));
-  var max = transformFn(new ol.Coordinate(this.maxX, this.maxY));
-  return new ol.CoverageArea(min.x, min.y, max.x, max.y, this.minZ, this.maxZ);
+  var extent = this.extent.transform(transformFn);
+  return new ol.CoverageArea(extent, this.minZ, this.maxZ);
 };
diff --git a/src/ol/tile/bingmaps.js b/src/ol/tile/bingmaps.js
index 84b4954f2a..3ebd9dbc78 100644
--- a/src/ol/tile/bingmaps.js
+++ b/src/ol/tile/bingmaps.js
@@ -162,10 +162,10 @@ ol.tilestore.BingMaps.prototype.handleImageryMetadataResponse =
             imageryProvider.coverageAreas,
             function(coverageArea) {
               var bbox = coverageArea.bbox;
+              var extent = new ol.Extent(bbox[0], bbox[1], bbox[2], bbox[3]);
               var minZ = coverageArea.zoomMin;
               var maxZ = coverageArea.zoomMax;
-              return new ol.CoverageArea(
-                  bbox[0], bbox[1], bbox[2], bbox[3], minZ, maxZ);
+              return new ol.CoverageArea(extent, minZ, maxZ);
             });
         return new ol.Attribution(html, coverageAreas, projection);
       });