diff --git a/src/ol/source/urltilesource.js b/src/ol/source/urltilesource.js
index febd9b10fa..b72958ddad 100644
--- a/src/ol/source/urltilesource.js
+++ b/src/ol/source/urltilesource.js
@@ -12,6 +12,7 @@ goog.require('ol.source.TileEvent');
 
 /**
  * @typedef {{attributions: (Array.<ol.Attribution>|undefined),
+ *            cacheSize: (number|undefined),
  *            extent: (ol.Extent|undefined),
  *            logo: (string|olx.LogoOptions|undefined),
  *            opaque: (boolean|undefined),