diff --git a/__tests__/html/attachment.combineAttachmentsAndText.html b/__tests__/html/attachment.combineAttachmentsAndText.html
index b790b5bd30..68b95a7ca8 100644
--- a/__tests__/html/attachment.combineAttachmentsAndText.html
+++ b/__tests__/html/attachment.combineAttachmentsAndText.html
@@ -1,4 +1,4 @@
-<!doctype html>
+<!DOCTYPE html>
 <html lang="en-US">
   <head>
     <link href="/assets/index.css" rel="stylesheet" type="text/css" />
