diff --git a/activesupport/lib/active_support/message_encryptor.rb b/activesupport/lib/active_support/message_encryptor.rb
index 347af9dc76..51fa626b45 100644
--- a/activesupport/lib/active_support/message_encryptor.rb
+++ b/activesupport/lib/active_support/message_encryptor.rb
@@ -1,4 +1,5 @@
 require 'openssl'
+require 'active_support/base64'
 
 module ActiveSupport
   # MessageEncryptor is a simple way to encrypt values which get stored somewhere