diff --git a/externs/olx.js b/externs/olx.js
index a569214a05..9f972d224d 100644
--- a/externs/olx.js
+++ b/externs/olx.js
@@ -49,94 +49,6 @@ olx.render.State.prototype.resolution;
 olx.render.State.prototype.rotation;
 
 
-/**
- * @typedef {{attributions: (ol.AttributionLike|undefined),
- *     distance: (number|undefined),
- *     extent: (ol.Extent|undefined),
- *     format: (ol.format.Feature|undefined),
- *     geometryFunction: (undefined|function(module:ol/Feature~Feature):module:ol/geom/Point~Point),
- *     projection: ol.ProjectionLike,
- *     source: ol.source.Vector,
- *     wrapX: (boolean|undefined)}}
- */
-olx.source.ClusterOptions;
-
-
-/**
- * Attributions.
- * @type {ol.AttributionLike|undefined}
- * @api
- */
-olx.source.ClusterOptions.prototype.attributions;
-
-
-/**
- * Minimum distance in pixels between clusters. Default is `20`.
- * @type {number|undefined}
- * @api
- */
-olx.source.ClusterOptions.prototype.distance;
-
-
-/**
- * Extent.
- * @type {ol.Extent|undefined}
- * @api
- */
-olx.source.ClusterOptions.prototype.extent;
-
-
-/**
- * Function that takes an {@link module:ol/Feature~Feature} as argument and returns an
- * {@link module:ol/geom/Point~Point} as cluster calculation point for the feature. When a
- * feature should not be considered for clustering, the function should return
- * `null`. The default, which works when the underyling source contains point
- * features only, is
- * ```js
- * function(feature) {
- *   return feature.getGeometry();
- * }
- * ```
- * See {@link module:ol/geom/Polygon~Polygon#getInteriorPoint} for a way to get a cluster
- * calculation point for polygons.
- * @type {undefined|function(module:ol/Feature~Feature):module:ol/geom/Point~Point}
- * @api
- */
-olx.source.ClusterOptions.prototype.geometryFunction;
-
-
-/**
- * Format.
- * @type {ol.format.Feature|undefined}
- * @api
- */
-olx.source.ClusterOptions.prototype.format;
-
-
-/**
- * Projection.
- * @type {ol.ProjectionLike}
- * @api
- */
-olx.source.ClusterOptions.prototype.projection;
-
-
-/**
- * Source.
- * @type {ol.source.Vector}
- * @api
- */
-olx.source.ClusterOptions.prototype.source;
-
-
-/**
- * WrapX. Default is true
- * @type {boolean|undefined}
- * @api
- */
-olx.source.ClusterOptions.prototype.wrapX;
-
-
 /**
  * @typedef {{preemptive: (boolean|undefined),
  *     jsonp: (boolean|undefined),
diff --git a/src/ol/source/Cluster.js b/src/ol/source/Cluster.js
index d337275a83..0001a3c008 100644
--- a/src/ol/source/Cluster.js
+++ b/src/ol/source/Cluster.js
@@ -12,6 +12,31 @@ import {buffer, createEmpty, createOrUpdateFromCoordinate} from '../extent.js';
 import Point from '../geom/Point.js';
 import VectorSource from '../source/Vector.js';
 
+/**
+ * @typedef {Object} Options
+ * @property {ol.AttributionLike} [attributions] Attributions.
+ * @property {number} [distance=20] Minimum distance in pixels between clusters.
+ * @property {ol.Extent} [extent] Extent.
+ * @property {ol.format.Feature} [format] Format.
+ * @property {function(module:ol/Feature~Feature):module:ol/geom/Point~Point} [geometryFunction]
+ * Function that takes an {@link module:ol/Feature~Feature} as argument and returns an
+ * {@link module:ol/geom/Point~Point} as cluster calculation point for the feature. When a
+ * feature should not be considered for clustering, the function should return
+ * `null`. The default, which works when the underyling source contains point
+ * features only, is
+ * ```js
+ * function(feature) {
+ *   return feature.getGeometry();
+ * }
+ * ```
+ * See {@link module:ol/geom/Polygon~Polygon#getInteriorPoint} for a way to get a cluster
+ * calculation point for polygons.
+ * @property {ol.ProjectionLike} projection Projection.
+ * @property {ol.source.Vector} source Source.
+ * @property {boolean} [wrapX=true] Whether to wrap the world horizontally.
+ */
+
+
 /**
  * @classdesc
  * Layer source to cluster vector data. Works out of the box with point
@@ -19,7 +44,7 @@ import VectorSource from '../source/Vector.js';
  * considered for clustering, a custom `geometryFunction` can be defined.
  *
  * @constructor
- * @param {olx.source.ClusterOptions} options Constructor options.
+ * @param {module:ol/source/Cluster~Options=} options Cluster options.
  * @extends {ol.source.Vector}
  * @api
  */