diff --git a/lib/mongo_mapper/bson_id.rb b/lib/mongo_mapper/bson_id.rb
index 6a6b1928e..966edbf1c 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