diff --git a/lib/mongo_mapper/bson_id.rb b/lib/mongo_mapper/bson_id.rb
index 6a6b1928ee3094c22d85e23e9a73fa1b0fbe415d..966edbf1ce6f5c8d10b6376ec27a742a41b11b8e 100644
--- a/lib/mongo_mapper/bson_id.rb
+++ b/lib/mongo_mapper/bson_id.rb
@@ -1,9 +1,9 @@
 class String
   def to_id
-    BSON::ObjectId self
+    BSON::ObjectID self
   end
 end
-class BSON::ObjectId
+class BSON::ObjectID
   def to_id
     self
   end