diff --git a/src/ol/deviceorientation.js b/src/ol/deviceorientation.js
index 1b1b25f09a..8e40fdd47d 100644
--- a/src/ol/deviceorientation.js
+++ b/src/ol/deviceorientation.js
@@ -33,7 +33,7 @@ ol.DeviceOrientation = function(opt_options) {
 
   /**
    * @private
-   * @type {?number}
+   * @type {goog.events.Key}
    */
   this.listenerKey_ = null;
 
diff --git a/src/ol/map.js b/src/ol/map.js
index 5c4fad875c..6ac5afa782 100644
--- a/src/ol/map.js
+++ b/src/ol/map.js
@@ -196,7 +196,7 @@ ol.Map = function(options) {
 
   /**
    * @private
-   * @type {?number}
+   * @type {goog.events.Key}
    */
   this.viewPropertyListenerKey_ = null;
 
diff --git a/src/ol/object.js b/src/ol/object.js
index ace988c391..adcc43ccec 100644
--- a/src/ol/object.js
+++ b/src/ol/object.js
@@ -118,7 +118,7 @@ ol.Object.getGetterName = function(key) {
 
 /**
  * @param {ol.Object} obj Object.
- * @return {Object.<string, ?number>} Listeners.
+ * @return {Object.<string, goog.events.Key>} Listeners.
  */
 ol.Object.getListeners = function(obj) {
   return obj[ol.ObjectProperty.BINDINGS] ||
@@ -235,7 +235,7 @@ ol.Object.prototype.notifyInternal_ = function(key) {
  * @param {Function} listener The listener function.
  * @param {Object=} opt_scope Object is whose scope to call
  *     the listener.
- * @return {?number} Unique key for the listener.
+ * @return {goog.events.Key} Unique key for the listener.
  */
 ol.Object.prototype.on = function(type, listener, opt_scope) {
   return goog.events.listen(this, type, listener, false, opt_scope);
@@ -248,7 +248,7 @@ ol.Object.prototype.on = function(type, listener, opt_scope) {
  * @param {Function} listener The listener function.
  * @param {Object=} opt_scope Object is whose scope to call
  *     the listener.
- * @return {?number} Unique key for the listener.
+ * @return {goog.events.Key} Unique key for the listener.
  */
 ol.Object.prototype.once = function(type, listener, opt_scope) {
   return goog.events.listenOnce(this, type, listener, false, opt_scope);