diff --git a/src/ol/tile/tilestore.js b/src/ol/tile/tilestore.js
index cf0a7108da..5a78edcada 100644
--- a/src/ol/tile/tilestore.js
+++ b/src/ol/tile/tilestore.js
@@ -85,7 +85,7 @@ ol.TileStore.prototype.getTile = function(tileCoord) {
 
 /**
  * @param {ol.TileCoord} tileCoord Tile coordinate.
- * @return {string} Tile coord URL.
+ * @return {string|undefined} Tile URL.
  */
 ol.TileStore.prototype.getTileCoordUrl = function(tileCoord) {
   return this.tileUrlFunction_(tileCoord);
diff --git a/src/ol/tile/tileurlfunction.js b/src/ol/tile/tileurlfunction.js
index 8135a644c6..38ef5179b9 100644
--- a/src/ol/tile/tileurlfunction.js
+++ b/src/ol/tile/tileurlfunction.js
@@ -6,7 +6,7 @@ goog.require('ol.TileCoord');
 
 
 /**
- * @typedef {function(ol.TileCoord): string|undefined}
+ * @typedef {function(ol.TileCoord): (string|undefined)}
  */
 ol.TileUrlFunctionType;