diff --git a/lib/lib.es5.d.ts b/lib/lib.es5.d.ts
index 3f495ed40a9..07ffe74c05f 100644
--- a/lib/lib.es5.d.ts
+++ b/lib/lib.es5.d.ts
@@ -792,8 +792,7 @@ interface Date {
 
 interface DateConstructor {
     new(): Date;
-    new(value: number): Date;
-    new(value: string): Date;
+    new(value: string | number): Date;
     new(year: number, month: number, date?: number, hours?: number, minutes?: number, seconds?: number, ms?: number): Date;
     (): string;
     readonly prototype: Date;
diff --git a/src/lib/es2015.core.d.ts b/src/lib/es2015.core.d.ts
index eef20591a84..68be040c29d 100644
--- a/src/lib/es2015.core.d.ts
+++ b/src/lib/es2015.core.d.ts
@@ -69,7 +69,7 @@ interface ArrayConstructor {
 }
 
 interface DateConstructor {
-    new (value: Date): Date;
+    new (value: number | string | Date): Date;
 }
 
 interface Function {