diff --git a/src/ol/tilegrid/tilegrid.js b/src/ol/tilegrid/tilegrid.js
index c042ef5baf..37fd841a9a 100644
--- a/src/ol/tilegrid/tilegrid.js
+++ b/src/ol/tilegrid/tilegrid.js
@@ -492,6 +492,7 @@ ol.tilegrid.TileGrid.prototype.getFullTileRange = function(z) {
  *     If 1, the nearest lower resolution will be used. If -1, the nearest
  *     higher resolution will be used. Default is 0.
  * @return {number} Z.
+ * @api
  */
 ol.tilegrid.TileGrid.prototype.getZForResolution = function(
     resolution, opt_direction) {