diff --git a/src/ol/renderer/canvas/canvasmaprenderer.js b/src/ol/renderer/canvas/canvasmaprenderer.js
index 9a20c3bedd8..1df47410659 100644
--- a/src/ol/renderer/canvas/canvasmaprenderer.js
+++ b/src/ol/renderer/canvas/canvasmaprenderer.js
@@ -13,6 +13,7 @@ goog.require('ol.layer.Tile');
 goog.require('ol.layer.Vector');
 goog.require('ol.renderer.Map');
 goog.require('ol.renderer.canvas.ImageLayer');
+goog.require('ol.renderer.canvas.Layer');
 goog.require('ol.renderer.canvas.TileLayer');
 goog.require('ol.renderer.canvas.VectorLayer');
 goog.require('ol.source.State');
@@ -114,8 +115,8 @@ ol.renderer.canvas.Map.prototype.renderFrame = function(frameState) {
   for (i = 0, ii = layersArray.length; i < ii; ++i) {
 
     layer = layersArray[i];
-    layerRenderer =
-        /** @type {ol.renderer.canvas.Layer} */ (this.getLayerRenderer(layer));
+    layerRenderer = this.getLayerRenderer(layer);
+    goog.asserts.assertInstanceof(layerRenderer, ol.renderer.canvas.Layer);
     layerState = layerStates[goog.getUid(layer)];
     if (!layerState.visible ||
         layerState.sourceState != ol.source.State.READY ||
diff --git a/src/ol/renderer/dom/dommaprenderer.js b/src/ol/renderer/dom/dommaprenderer.js
index f05b9326de2..2e135d5192c 100644
--- a/src/ol/renderer/dom/dommaprenderer.js
+++ b/src/ol/renderer/dom/dommaprenderer.js
@@ -9,6 +9,7 @@ goog.require('ol.layer.Image');
 goog.require('ol.layer.Tile');
 goog.require('ol.renderer.Map');
 goog.require('ol.renderer.dom.ImageLayer');
+goog.require('ol.renderer.dom.Layer');
 goog.require('ol.renderer.dom.TileLayer');
 goog.require('ol.source.State');
 
@@ -93,8 +94,8 @@ ol.renderer.dom.Map.prototype.renderFrame = function(frameState) {
   var layerKey;
   for (layerKey in this.getLayerRenderers()) {
     if (!(layerKey in layerStates)) {
-      layerRenderer = /** @type {ol.renderer.dom.Layer} */
-          (this.getLayerRendererByKey(layerKey));
+      layerRenderer = this.getLayerRendererByKey(layerKey);
+      goog.asserts.assertInstanceof(layerRenderer, ol.renderer.dom.Layer);
       goog.dom.removeNode(layerRenderer.getTarget());
     }
   }