diff --git a/README.rst b/README.rst
index 693c35b..e79b97e 100644
--- a/README.rst
+++ b/README.rst
@@ -11,7 +11,7 @@ Build message:
    >>> message = emails.html(html="<p>Hi!<br>Here is your receipt...",
                           subject="Your receipt No. 567098123",
                           mail_from=('Some Store', 'store@somestore.com'))
-   >>> message.attach(data=open('bill.pdf'), filename='bill.pdf')
+   >>> message.attach(data=open('bill.pdf', 'rb'), filename='bill.pdf')
 
 send message and get response from smtp server: