diff --git a/knockout.postbox/knockout-postbox.d.ts b/knockout.postbox/knockout-postbox.d.ts
index 65f0bbf132..1dfda1a255 100644
--- a/knockout.postbox/knockout-postbox.d.ts
+++ b/knockout.postbox/knockout-postbox.d.ts
@@ -9,6 +9,7 @@ interface KnockoutPostBox {
     subscribe<T>(topic: string, handler: (value: T) => void , target?: any): KnockoutSubscription;
     publish<T>(topic: string, value?: T): void;
     defaultComparer<T>(newValue: T, oldValue: T): boolean;
+    serializer: (object: any) => string;
 }
 
 interface KnockoutObservable<T> {
@@ -29,4 +30,4 @@ interface KnockoutObservableArray<T> {
 
 interface KnockoutStatic {
     postbox: KnockoutPostBox;
-}
\ No newline at end of file
+}