diff --git a/mongodb/index.d.ts b/mongodb/index.d.ts
index f16d5cce0d..49f092a0f1 100644
--- a/mongodb/index.d.ts
+++ b/mongodb/index.d.ts
@@ -426,6 +426,8 @@ export class ObjectID {
     getTimestamp(): Date;
     // Returns the ObjectID id as a 24 byte hex string representation
     toHexString(): string;
+    // Returns the ObjectID id as a 24 byte hex string representation
+    toString(): string;
 }
 
 // Class documentation : http://mongodb.github.io/node-mongodb-native/2.1/api/Binary.html