diff --git a/src/ol/renderer/maprenderer.js b/src/ol/renderer/maprenderer.js
index adc4de270f..201f0486ad 100644
--- a/src/ol/renderer/maprenderer.js
+++ b/src/ol/renderer/maprenderer.js
@@ -133,6 +133,17 @@ ol.renderer.Map.prototype.getLayerRenderer = function(layer) {
 };
 
 
+/**
+ * @param {string} layerKey Layer key.
+ * @protected
+ * @return {ol.renderer.Layer} Layer renderer.
+ */
+ol.renderer.Map.prototype.getLayerRendererByKey = function(layerKey) {
+  goog.asserts.assert(layerKey in this.layerRenderers_);
+  return this.layerRenderers_[layerKey];
+};
+
+
 /**
  * @protected
  * @return {Object.<number, ol.renderer.Layer>} Layer renderers.