diff --git a/actionmailer/CHANGELOG b/actionmailer/CHANGELOG
index 2ac696fba7..353472c775 100644
--- a/actionmailer/CHANGELOG
+++ b/actionmailer/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Allow specific "multipart/xxx" content-type to be set on multipart messages #1412 [Flurin Egger]
+
 * Unquoted @ characters in headers are now accepted in spite of RFC 822 #1206
 
 * Helper support (borrowed from ActionPack)
diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index 7154dbdc93..a8880146af 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -278,6 +278,8 @@ module ActionMailer #:nodoc:
             part = (TMail::Mail === p ? p : p.to_mail(self))
             m.parts << part
           end
+          
+          m.set_content_type(content_type, nil, { "charset" => charset }) if content_type =~ /multipart/
         end
 
         @mail = m
diff --git a/actionmailer/test/mail_service_test.rb b/actionmailer/test/mail_service_test.rb
index 8eb001ab25..7efd044796 100755
--- a/actionmailer/test/mail_service_test.rb
+++ b/actionmailer/test/mail_service_test.rb
@@ -94,12 +94,13 @@ class TestMailer < ActionMailer::Base
     @charset    = "utf-8"
   end
 
-  def explicitly_multipart_example(recipient)
-    @recipients = recipient
-    @subject    = "multipart example"
-    @from       = "test@example.com"
-    @sent_on    = Time.local 2004, 12, 12
-    @body       = "plain text default"
+  def explicitly_multipart_example(recipient, ct=nil)
+    recipients   recipient
+    subject      "multipart example"
+    from         "test@example.com"
+    sent_on      Time.local(2004, 12, 12)
+    body         "plain text default"
+    content_type ct if ct
 
     part "text/html" do |p|
       p.charset = "iso-8859-1"
@@ -462,6 +463,7 @@ EOF
   def test_explicitly_multipart_messages
     mail = TestMailer.create_explicitly_multipart_example(@recipient)
     assert_equal 3, mail.parts.length
+    assert_nil mail.content_type
     assert_equal "text/plain", mail.parts[0].content_type
 
     assert_equal "text/html", mail.parts[1].content_type
@@ -475,6 +477,19 @@ EOF
     assert_nil mail.parts[2].sub_header("content-type", "charset")
   end
 
+  def test_explicitly_multipart_with_content_type
+    mail = TestMailer.create_explicitly_multipart_example(@recipient,
+      "multipart/alternative")
+    assert_equal 3, mail.parts.length
+    assert_equal "multipart/alternative", mail.content_type
+  end
+
+  def test_explicitly_multipart_with_invalid_content_type
+    mail = TestMailer.create_explicitly_multipart_example(@recipient, "text/xml")
+    assert_equal 3, mail.parts.length
+    assert_nil mail.content_type
+  end
+
   def test_implicitly_multipart_messages
     mail = TestMailer.create_implicitly_multipart_example(@recipient)
     assert_equal 2, mail.parts.length