diff --git a/knockout/knockout.d.ts b/knockout/knockout.d.ts
index eaae8bee1..c20207199 100644
--- a/knockout/knockout.d.ts
+++ b/knockout/knockout.d.ts
@@ -135,8 +135,8 @@ interface KnockoutAllBindingsAccessor {
 }
 
 interface KnockoutBindingHandler {
-    init?: (element: any, valueAccessor: () => any, allBindingsAccessor: KnockoutAllBindingsAccessor, viewModel: any, bindingContext: KnockoutBindingContext) => void | { controlsDescendantBindings: boolean; };
-    update?: (element: any, valueAccessor: () => any, allBindingsAccessor: KnockoutAllBindingsAccessor, viewModel: any, bindingContext: KnockoutBindingContext) => void;
+    init?: (element: any, valueAccessor: () => any, allBindingsAccessor?: KnockoutAllBindingsAccessor, viewModel?: any, bindingContext?: KnockoutBindingContext) => void | { controlsDescendantBindings: boolean; };
+    update?: (element: any, valueAccessor: () => any, allBindingsAccessor?: KnockoutAllBindingsAccessor, viewModel?: any, bindingContext?: KnockoutBindingContext) => void;
     options?: any;
     preprocess?: (value: string, name: string, addBindingCallback?: (name: string, value: string) => void) => string;
 }