diff --git a/src/Mailgun/Messages/README.md b/src/Mailgun/Messages/README.md
index 075b554..34cab45 100644
--- a/src/Mailgun/Messages/README.md
+++ b/src/Mailgun/Messages/README.md
@@ -65,7 +65,7 @@ Available Functions
 
 `string setHtmlBody(string $htmlBody)`  
 
-`bool addAttachment(string $attachmentPath)`  
+`bool addAttachment(string $attachmentPath, $attachmentName = null)`  
 
 `bool addInlineImage(string $inlineImagePath)`