diff --git a/src/ol/layer/layer.js b/src/ol/layer/layer.js
index 9d646e4e23..c85f845d68 100644
--- a/src/ol/layer/layer.js
+++ b/src/ol/layer/layer.js
@@ -3,6 +3,7 @@ goog.provide('ol.layer.Layer');
 goog.require('goog.events');
 goog.require('goog.events.EventType');
 goog.require('goog.object');
+goog.require('ol');
 goog.require('ol.Object');
 goog.require('ol.layer.Base');
 goog.require('ol.layer.LayerProperty');
@@ -52,7 +53,7 @@ ol.layer.Layer = function(options) {
    */
   this.sourceChangeKey_ = null;
 
-  if (goog.isDef(options.map)) {
+  if (options.map) {
     this.setMap(options.map);
   }
 
@@ -60,7 +61,7 @@ ol.layer.Layer = function(options) {
       ol.Object.getChangeEventType(ol.layer.LayerProperty.SOURCE),
       this.handleSourcePropertyChange_, false, this);
 
-  var source = goog.isDef(options.source) ? options.source : null;
+  var source = options.source ? options.source : null;
   this.setSource(source);
 };
 goog.inherits(ol.layer.Layer, ol.layer.Base);
@@ -84,7 +85,7 @@ ol.layer.Layer.visibleAtResolution = function(layerState, resolution) {
  * @inheritDoc
  */
 ol.layer.Layer.prototype.getLayersArray = function(opt_array) {
-  var array = goog.isDef(opt_array) ? opt_array : [];
+  var array = opt_array ? opt_array : [];
   array.push(this);
   return array;
 };
@@ -94,7 +95,7 @@ ol.layer.Layer.prototype.getLayersArray = function(opt_array) {
  * @inheritDoc
  */
 ol.layer.Layer.prototype.getLayerStatesArray = function(opt_states) {
-  var states = goog.isDef(opt_states) ? opt_states : [];
+  var states = opt_states ? opt_states : [];
   states.push(this.getLayerState());
   return states;
 };
@@ -108,7 +109,7 @@ ol.layer.Layer.prototype.getLayerStatesArray = function(opt_states) {
  */
 ol.layer.Layer.prototype.getSource = function() {
   var source = this.get(ol.layer.LayerProperty.SOURCE);
-  return goog.isDef(source) ?
+  return ol.isDef(source) ?
       /** @type {ol.source.Source} */ (source) : null;
 };