diff --git a/object-assign/object-assign-tests.ts b/object-assign/object-assign-tests.ts
index 53dfd5e707..6b9a898ed4 100644
--- a/object-assign/object-assign-tests.ts
+++ b/object-assign/object-assign-tests.ts
@@ -1,17 +1,79 @@
 /// <reference path="object-assign.d.ts" />
 import objectAssign = require("object-assign");
 
-function assign1() {
-  var result = objectAssign({hello: "world"});
-  return result;
+interface Target {
+  hellow: string;
 }
 
-function assign2() {
-  var result = objectAssign({hello: "world"}, {hello: "worlds", second: "extra"});
-  return result;
+interface Source1 {
+  source1: string;
 }
 
-function assign3() {
-  var result = objectAssign({hello: "world"}, {hello: "worlds", second: "extra"}, {hello: "stop", the: "spinning"});
-  return result;
+interface Result extends Target, Source1 {
+  
 }
+
+interface Source2 {
+  source2: string;
+}
+
+interface Result2 extends Result, Source2 {
+  
+}
+
+interface Source3 {
+  source3: string;
+}
+
+interface Result3 extends Result2, Source3 {
+  
+}
+
+interface Source4 {
+  source4: string;
+}
+
+interface Result4 extends Result3, Source4 {
+  
+}
+
+interface Source5 {
+  source5: string;
+}
+
+interface Result5 extends Result4, Source5 {
+  
+}
+
+function assign1(): Result {
+  return objectAssign({hellow: "world"}, {source1: "U"});
+}
+
+function assign2(): Result2 {
+  return objectAssign({hellow: "world"}, {source1: "U"}, {source2: "V"});
+}
+
+function assign3(): Result3 {
+  return objectAssign({hellow: "world"}, {source1: "U"}, {source2: "V"}, {source3: "W"});
+}
+
+function assign4(): Result4 {
+  return objectAssign({hellow: "world"}, {source1: "U"}, {source2: "V"}, {source3: "W"}, {source4: "Q"});
+}
+
+function assign5(): Result5 {
+  return objectAssign({hellow: "world"}, {source1: "U"}, {source2: "V"}, {source3: "W"}, {source4: "Q"}, {source5: "R"});
+}
+
+function assign() {
+  return objectAssign({hellow: "world"}, {source1: "U"}, {source2: "V"}, {source3: "W"}, {source4: "Q"}, {source5: "R"}, {
+    hellow: "hellow",
+    source1: "source1",
+    source2: "source2",
+    source3: "source3",
+    source4: "source4",
+    source5: "source5",
+    generic: "any"
+  });
+}
+
diff --git a/object-assign/object-assign.d.ts b/object-assign/object-assign.d.ts
index 52ef486c72..c3f92b7592 100644
--- a/object-assign/object-assign.d.ts
+++ b/object-assign/object-assign.d.ts
@@ -4,6 +4,11 @@
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 declare module "object-assign" {
+  function objectAssign<T, U>(target: T, source: U): T & U;
+  function objectAssign<T, U, V>(target: T, source1: U, source2: V): T & U & V;
+  function objectAssign<T, U, V, W>(target: T, source1: U, source2: V, source3: W): T & U & V & W;
+  function objectAssign<T, U, V, W, Q>(target: T, source1: U, source2: V, source3: W, source4: Q): T & U & V & W & Q;
+  function objectAssign<T, U, V, W, Q, R>(target: T, source1: U, source2: V, source3: W, source4: Q, source5: R): T & U & V & W & Q & R;
   function objectAssign(target: any, ...sources: any[]): any;
   export = objectAssign;
 }