diff --git a/mongodb/mongodb.d.ts b/mongodb/mongodb.d.ts
index cc2de59bed..0805e832ab 100644
--- a/mongodb/mongodb.d.ts
+++ b/mongodb/mongodb.d.ts
@@ -109,7 +109,7 @@ declare module "mongodb" {
   // Class documentation : http://mongodb.github.io/node-mongodb-native/api-bson-generated/objectid.html
   // Last update: doc. version 1.3.13 (28.08.2013)
   export class ObjectID {
-    constructor (s: string);
+    constructor (s?: string);
 
     // Returns the ObjectID id as a 24 byte hex string representation
     public toHexString() : string;