diff --git a/src/ol/view.js b/src/ol/view.js
index 096dcbf363..e88dc759cd 100644
--- a/src/ol/view.js
+++ b/src/ol/view.js
@@ -662,7 +662,7 @@ ol.View.prototype.getResolutions = function() {
 /**
  * Get the resolution for a provided extent (in map units) and size (in pixels).
  * @param {ol.Extent} extent Extent.
- * @param {ol.Size} opt_size Box pixel size.
+ * @param {ol.Size=} opt_size Box pixel size.
  * @return {number} The resolution at which the provided extent will render at
  *     the given size.
  * @api