diff --git a/app/views/report_mailer/moderator_report.html.erb b/app/views/report_mailer/moderator_report.html.erb
index 03c52c026..ad92347d5 100644
--- a/app/views/report_mailer/moderator_report.html.erb
+++ b/app/views/report_mailer/moderator_report.html.erb
@@ -1,3 +1,6 @@
+<!doctype html>
+<html>
+<body>
 <h1>Moderator Report For <%= Date.today %></h1>
 
 <div style="margin-bottom: 2em;">
@@ -28,3 +31,5 @@
   </tbody>
 </table>
 </div>
+</body>
+</html>
\ No newline at end of file
diff --git a/app/views/user_mailer/dmail_notice.html.erb b/app/views/user_mailer/dmail_notice.html.erb
index 2c0347e89..99dbfa655 100644
--- a/app/views/user_mailer/dmail_notice.html.erb
+++ b/app/views/user_mailer/dmail_notice.html.erb
@@ -1,3 +1,6 @@
+<!doctype html>
+<html>
+<body>
 <p><%= h @dmail.from.name %> said:</p>
 
 <div>
@@ -5,3 +8,5 @@
 </div>
 
 <p><%= link_to "View message", dmail_path(@dmail, :host => Danbooru.config.hostname, :only_path => false) %></p>
+</body>
+</html>
\ No newline at end of file
diff --git a/app/views/user_mailer/upgrade.html.erb b/app/views/user_mailer/upgrade.html.erb
index 6c0513533..f01e49491 100644
--- a/app/views/user_mailer/upgrade.html.erb
+++ b/app/views/user_mailer/upgrade.html.erb
@@ -1 +1,6 @@
+<!doctype html>
+<html>
+<body>
 <p>You can upgrade your account by sending $20 USD via Paypal to <%= mail_to Danbooru.config.upgrade_account_email %>. Be sure to include your username.</p>
+</body>
+</html>
\ No newline at end of file
diff --git a/app/views/user_mailer/upgrade_fail.html.erb b/app/views/user_mailer/upgrade_fail.html.erb
index 4ec03acfd..db0bc2e13 100644
--- a/app/views/user_mailer/upgrade_fail.html.erb
+++ b/app/views/user_mailer/upgrade_fail.html.erb
@@ -1 +1,6 @@
-<p>Account upgrades are currently disabled.</p>
\ No newline at end of file
+<!doctype html>
+<html>
+<body>
+<p>Account upgrades are currently disabled.</p>
+</body>
+</html>
\ No newline at end of file
