diff --git a/packages/base/src/widget.ts b/packages/base/src/widget.ts
index f58d9ded0f..174698b856 100644
--- a/packages/base/src/widget.ts
+++ b/packages/base/src/widget.ts
@@ -563,12 +563,13 @@ export class WidgetModel extends Backbone.Model {
    */
   serialize(state: Dict<any>): JSONObject {
     const serializers =
-      (this.constructor as typeof WidgetModel).serializers || {};
+      (this.constructor as typeof WidgetModel).serializers || JSONExt.emptyObject;
     for (const k of Object.keys(state)) {
       try {
-        let { serialize, deserialize } = serializers[k] || JSONExt.emptyObject;
+        const keySerializers = serializers[k] || JSONExt.emptyObject;
+        let { serialize } = keySerializers;
 
-        if (serialize == null && deserialize === unpack_models) {
+        if (serialize == null && keySerializers.deserialize === unpack_models) {
           // handle https://github.com/jupyter-widgets/ipywidgets/issues/3735
           serialize = pack_models;
         }