diff --git a/knockout/knockout.d.ts b/knockout/knockout.d.ts
index aa6044e9f4..b41846ca55 100644
--- a/knockout/knockout.d.ts
+++ b/knockout/knockout.d.ts
@@ -68,11 +68,8 @@ interface KnockoutComputedStatic {
     (options?: any): KnockoutComputed<any>;
 }
 
-interface KnockoutComputed<T> extends KnockoutSubscribable<T>, KnockoutComputedFunctions<T> {
-	(): T;
-	(value: T): void;
-
-	peek(): T;
+interface KnockoutComputed<T> extends KnockoutObservable<T>, KnockoutComputedFunctions<T> {
+	
 	dispose(): void;
 	isActive(): boolean;
 	getDependenciesCount(): number;
@@ -100,8 +97,8 @@ interface KnockoutObservable<T> extends KnockoutSubscribable<T>, KnockoutObserva
 	(value: T): void;
 
 	peek(): T;
-	valueHasMutated(): void;
-	valueWillMutate(): void;
+	valueHasMutated?:{(): void;};
+	valueWillMutate?:{(): void;};
     extend(requestedExtenders: { [key: string]: any; }): KnockoutObservable<T>;
 }
 
diff --git a/knockout/tests/knockout-tests.ts b/knockout/tests/knockout-tests.ts
index b0755c12af..fb39552415 100644
--- a/knockout/tests/knockout-tests.ts
+++ b/knockout/tests/knockout-tests.ts
@@ -570,4 +570,17 @@ function test_misc() {
     ko.utils.domNodeDisposal.addDisposeCallback(element, function () {
         $(element).datepicker("destroy");
     });
+	
+	this.observableFactory = function(): KnockoutObservable<number>{
+	    if (true) {
+			return ko.computed({
+				read:function(){ 
+					return 3; 
+				}
+			});
+		} else {
+			return ko.observable(3);
+		}
+	}
+	
 }
\ No newline at end of file