diff --git a/knockout/knockout.d.ts b/knockout/knockout.d.ts
index 3ac8d0a0e..c68c38aff 100644
--- a/knockout/knockout.d.ts
+++ b/knockout/knockout.d.ts
@@ -442,7 +442,7 @@ interface KnockoutStatic {
     cleanNode(node: Element): Element;
     renderTemplate(template: Function, viewModel: any, options?: any, target?: any, renderMode?: any): any;
     renderTemplate(template: string, viewModel: any, options?: any, target?: any, renderMode?: any): any;
-	unwrap(value: any): any;
+	unwrap<T>(value: KnockoutObservable<T> | T): T;
 
 	computedContext: KnockoutComputedContext;
 
diff --git a/knockout/tests/knockout-tests.ts b/knockout/tests/knockout-tests.ts
index 64a91d199..78d464f07 100644
--- a/knockout/tests/knockout-tests.ts
+++ b/knockout/tests/knockout-tests.ts
@@ -648,4 +648,11 @@ function test_Components() {
         // Empty config for registering custom elements that are handled by name convention
 		ko.components.register('name', { /* No config needed */ });
     }
+}
+
+function testUnwrapUnion() {
+    
+    var possibleObs: KnockoutObservable<number> | number;
+    var num = ko.unwrap(possibleObs);
+
 }
\ No newline at end of file