diff --git a/src/ol/source/vector.js b/src/ol/source/vector.js
index 78a0d5a338..e1e88b30cf 100644
--- a/src/ol/source/vector.js
+++ b/src/ol/source/vector.js
@@ -610,7 +610,8 @@ ol.source.Vector.prototype.getClosestFeatureToCoordinate = function(coordinate,
  *
  * This method is not available when the source is configured with
  * `useSpatialIndex` set to `false`.
- * @param {ol.Extent=} opt_extent Destination extent.
+ * @param {ol.Extent=} opt_extent Destination extent. If provided, no new extent
+ *     will be created. Instead, that extent's coordinates will be overwritten.
  * @return {!ol.Extent} Extent.
  * @api
  */