diff --git a/src/ol/Collection.js b/src/ol/Collection.js
index 401e19d256..5b01dfb1a7 100644
--- a/src/ol/Collection.js
+++ b/src/ol/Collection.js
@@ -71,6 +71,13 @@ class Collection extends BaseObject {
   constructor(opt_array, opt_options) {
     super();
 
+    /***
+     * @type {import("./Observable").OnSignature<import("./Observable").EventTypes, import("./events/Event.js").default> &
+     *   import("./Observable").OnSignature<import("./ObjectEventType").Types|'change:length', import("./Object").ObjectEvent> &
+     *   import("./Observable").OnSignature<'add'|'remove', CollectionEvent>}
+     */
+    this.on;
+
     const options = opt_options || {};
 
     /**
diff --git a/src/ol/Feature.js b/src/ol/Feature.js
index 6e8fdb8b3e..b56ab71ca7 100644
--- a/src/ol/Feature.js
+++ b/src/ol/Feature.js
@@ -69,6 +69,12 @@ class Feature extends BaseObject {
   constructor(opt_geometryOrProperties) {
     super();
 
+    /***
+     * @type {import("./Observable").OnSignature<import("./Observable").EventTypes, import("./events/Event.js").default> &
+     *   import("./Observable").OnSignature<import("./ObjectEventType").Types|'change:geometry', import("./Object").ObjectEvent>}
+     */
+    this.on;
+
     /**
      * @private
      * @type {number|string|undefined}