diff --git a/actionmailer/CHANGELOG.md b/actionmailer/CHANGELOG.md
index 9e9d07b386d01dbe13d0cb648d83f53e8cd68cca..41436de52621b4c3505ed59f2bd8bfe524b23700 100644
--- a/actionmailer/CHANGELOG.md
+++ b/actionmailer/CHANGELOG.md
@@ -1,3 +1,6 @@
-* No changes.
+* Fix ActionMailer testcase break with mail 2.5.4.
+  ActionMailer's testcase was wrong, because :transfer_encoding option was ignored in mail 2.5.3.
+
+  *kennyj*
 
 Please check [4-0-stable](https://github.com/rails/rails/blob/4-0-stable/actionmailer/CHANGELOG.md) for previous changes.
diff --git a/actionmailer/test/mailers/base_mailer.rb b/actionmailer/test/mailers/base_mailer.rb
index 20b6671283c8d1bbf3f25614e24b1f74fa97fea1..6584bf519505d8e8c89d027a87adda6e46e6c32b 100644
--- a/actionmailer/test/mailers/base_mailer.rb
+++ b/actionmailer/test/mailers/base_mailer.rb
@@ -38,7 +38,7 @@ def attachment_with_content(hash = {})
   end
 
   def attachment_with_hash
-    attachments['invoice.jpg'] = { data: "\312\213\254\232)b",
+    attachments['invoice.jpg'] = { data: ::Base64.encode64("\312\213\254\232)b"),
                                    mime_type: "image/x-jpg",
                                    transfer_encoding: "base64" }
     mail