diff --git a/Readme.md b/Readme.md
index 2bdf141..165e3c9 100644
--- a/Readme.md
+++ b/Readme.md
@@ -14,6 +14,7 @@ var Grid = require('gridfs-stream');
 
 // create or use an existing mongodb-native db instance
 var db = new mongo.Db('yourDatabaseName', new mongo.Server("127.0.0.1", 27017));
+// make sure the db instance is open before passing into `Grid`
 var gfs = Grid(db, mongo);
 
 // streaming to gridfs