diff --git a/externs/olx.js b/externs/olx.js
index 1fdab4d0a0..6bfc8de381 100644
--- a/externs/olx.js
+++ b/externs/olx.js
@@ -5,76 +5,6 @@
 let olx;
 
 
-/**
- * @typedef {{opacity: (number|undefined),
- *     visible: (boolean|undefined),
- *     extent: (ol.Extent|undefined),
- *     zIndex: (number|undefined),
- *     minResolution: (number|undefined),
- *     maxResolution: (number|undefined),
- *     layers: (Array.<ol.layer.Base>|ol.Collection.<ol.layer.Base>|undefined)}}
- */
-olx.layer.GroupOptions;
-
-
-/**
- * Opacity (0, 1). Default is `1`.
- * @type {number|undefined}
- * @api
- */
-olx.layer.GroupOptions.prototype.opacity;
-
-
-/**
- * Visibility. Default is `true`.
- * @type {boolean|undefined}
- * @api
- */
-olx.layer.GroupOptions.prototype.visible;
-
-
-/**
- * The bounding extent for layer rendering.  The layer will not be rendered
- * outside of this extent.
- * @type {ol.Extent|undefined}
- * @api
- */
-olx.layer.GroupOptions.prototype.extent;
-
-
-/**
- * The z-index for layer rendering.  At rendering time, the layers will be
- * ordered, first by Z-index and then by position. The default Z-index is 0.
- * @type {number|undefined}
- * @api
- */
-olx.layer.GroupOptions.prototype.zIndex;
-
-
-/**
- * The minimum resolution (inclusive) at which this layer will be visible.
- * @type {number|undefined}
- * @api
- */
-olx.layer.GroupOptions.prototype.minResolution;
-
-
-/**
- * The maximum resolution (exclusive) below which this layer will be visible.
- * @type {number|undefined}
- * @api
- */
-olx.layer.GroupOptions.prototype.maxResolution;
-
-
-/**
- * Child layers.
- * @type {Array.<ol.layer.Base>|ol.Collection.<ol.layer.Base>|undefined}
- * @api
- */
-olx.layer.GroupOptions.prototype.layers;
-
-
 /**
  * @typedef {{gradient: (Array.<string>|undefined),
  *     radius: (number|undefined),
diff --git a/src/ol/layer/Group.js b/src/ol/layer/Group.js
index eb11d36afd..1c684987c6 100644
--- a/src/ol/layer/Group.js
+++ b/src/ol/layer/Group.js
@@ -15,6 +15,22 @@ import {assign, clear} from '../obj.js';
 import SourceState from '../source/State.js';
 
 
+/**
+ * @typedef {Object} Options
+ * @property {number} [opacity=1] Opacity (0, 1).
+ * @property {boolean} [visible=true] Visibility.
+ * @property {ol.Extent} [extent] The bounding extent for layer rendering.  The layer will not be
+ * rendered outside of this extent.
+ * @property {number} [zIndex=0] The z-index for layer rendering.  At rendering time, the layers
+ * will be ordered, first by Z-index and then by position.
+ * @property {number} [minResolution] The minimum resolution (inclusive) at which this layer will be
+ * visible.
+ * @property {number} [maxResolution] The maximum resolution (exclusive) below which this layer will
+ * be visible.
+ * @property {(Array.<ol.layer.Base>|ol.Collection.<ol.layer.Base>)} [layers] Child layers.
+ */
+
+
 /**
  * @enum {string}
  * @private
@@ -32,13 +48,13 @@ const Property = {
  *
  * @constructor
  * @extends {module:ol/layer/Base~BaseLayer}
- * @param {olx.layer.GroupOptions=} opt_options Layer options.
+ * @param {module:ol/layer/Group~Options=} opt_options Layer options.
  * @api
  */
 const LayerGroup = function(opt_options) {
 
   const options = opt_options || {};
-  const baseOptions = /** @type {olx.layer.GroupOptions} */ (assign({}, options));
+  const baseOptions = /** @type {module:ol/layer/Group~Options} */ (assign({}, options));
   delete baseOptions.layers;
 
   let layers = options.layers;