diff --git a/src/ol/collection.js b/src/ol/collection.js
index 454b166cf4..cce5dc87cd 100644
--- a/src/ol/collection.js
+++ b/src/ol/collection.js
@@ -130,7 +130,7 @@ ol.Collection.prototype.getAt = function(index) {
  * @return {number} Length.
  */
 ol.Collection.prototype.getLength = function() {
-  return /** @type {number} */ this.get(ol.CollectionProperty.LENGTH);
+  return /** @type {number} */ (this.get(ol.CollectionProperty.LENGTH));
 };