diff --git a/knockout.validation/knockout.validation.d.ts b/knockout.validation/knockout.validation.d.ts
index d5e23a9ba1..8317f75526 100644
--- a/knockout.validation/knockout.validation.d.ts
+++ b/knockout.validation/knockout.validation.d.ts
@@ -142,6 +142,7 @@ interface KnockoutSubscribableFunctions<T> {
     isValid: KnockoutComputed<boolean>;
     isValidating: KnockoutObservable<boolean>;
     rules: KnockoutObservableArray<KnockoutValidationRule>;
+    isModified(val: boolean): void;
 }
 
 declare module "knockout.validation" {