diff --git a/actionmailer/CHANGELOG b/actionmailer/CHANGELOG
index 28c5803535..82497e324e 100644
--- a/actionmailer/CHANGELOG
+++ b/actionmailer/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Parse content-type apart before using it so that sub-parts of the header can be set correctly #2918 [Jamis Buck]
+
 * Make custom headers work in subparts #4034 [elan@bluemandrill.com]
 
 * Template paths with dot chars in them no longer mess up implicit template selection for multipart messages #3332 [Chad Fowler]
diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index 237e56ed0c..42d48fd5a6 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -413,14 +413,16 @@ module ActionMailer
         m.date = sent_on.to_time rescue sent_on if sent_on
         headers.each { |k, v| m[k] = v }
 
+        real_content_type, ctype_attrs = parse_content_type
+
         if @parts.empty?
-          m.set_content_type content_type, nil, { "charset" => charset }
+          m.set_content_type(real_content_type, nil, ctype_attrs)
           m.body = Utils.normalize_new_lines(body)
         else
           if String === body
             part = TMail::Mail.new
             part.body = Utils.normalize_new_lines(body)
-            part.set_content_type content_type, nil, { "charset" => charset }
+            part.set_content_type(real_content_type, nil, ctype_attrs)
             part.set_content_disposition "inline"
             m.parts << part
           end
@@ -430,7 +432,7 @@ module ActionMailer
             m.parts << part
           end
           
-          m.set_content_type(content_type, nil, { "charset" => charset }) if content_type =~ /multipart/
+          m.set_content_type(real_content_type, nil, ctype_attrs) if real_content_type =~ /multipart/
         end
 
         @mail = m
diff --git a/actionmailer/lib/action_mailer/part.rb b/actionmailer/lib/action_mailer/part.rb
index 7bdbf5345d..31f5b441e3 100644
--- a/actionmailer/lib/action_mailer/part.rb
+++ b/actionmailer/lib/action_mailer/part.rb
@@ -56,6 +56,8 @@ module ActionMailer
     def to_mail(defaults)
       part = TMail::Mail.new
 
+      real_content_type, ctype_attrs = parse_content_type(defaults)
+
       if @parts.empty?
         part.content_transfer_encoding = transfer_encoding || "quoted-printable"
         case (transfer_encoding || "").downcase
@@ -71,20 +73,20 @@ module ActionMailer
         # Also don't set filename and name when there is none (like in
         # non-attachment parts)
         if content_disposition == "attachment"
-          part.set_content_type(content_type || defaults.content_type, nil,
-            squish("charset" => nil, "name" => filename))
+          ctype_attrs.delete "charset"
+          part.set_content_type(real_content_type, nil,
+            squish("name" => filename).merge(ctype_attrs))
           part.set_content_disposition(content_disposition,
-            squish("filename" => filename))
+            squish("filename" => filename).merge(ctype_attrs))
         else
-          part.set_content_type(content_type || defaults.content_type, nil,
-            "charset" => (charset || defaults.charset))      
+          part.set_content_type(real_content_type, nil, ctype_attrs)
           part.set_content_disposition(content_disposition) 
         end        
       else
         if String === body
           part = TMail::Mail.new
           part.body = body
-          part.set_content_type content_type, nil, { "charset" => charset }
+          part.set_content_type(real_content_type, nil, ctype_attrs)
           part.set_content_disposition "inline"
           m.parts << part
         end
@@ -94,15 +96,16 @@ module ActionMailer
           part.parts << prt
         end
         
-        part.set_content_type(content_type, nil, { "charset" => charset }) if content_type =~ /multipart/
+        part.set_content_type(real_content_type, nil, ctype_attrs) if real_content_type =~ /multipart/
       end
 
-      @headers.each { |k,v| part[k] = v }
+      headers.each { |k,v| part[k] = v }
 
       part
     end
 
     private
+
       def squish(values={})
         values.delete_if { |k,v| v.nil? }
       end
diff --git a/actionmailer/lib/action_mailer/part_container.rb b/actionmailer/lib/action_mailer/part_container.rb
index 6199fe0b6e..3e3d6b9d4f 100644
--- a/actionmailer/lib/action_mailer/part_container.rb
+++ b/actionmailer/lib/action_mailer/part_container.rb
@@ -38,5 +38,14 @@ module ActionMailer
       part(params, &block)
     end
 
+    private
+    
+      def parse_content_type(defaults=nil)
+        return [defaults && defaults.content_type, {}] if content_type.blank?
+        ctype, *attrs = content_type.split(/;\s*/)
+        attrs = attrs.inject({}) { |h,s| k,v = s.split(/=/, 2); h[k] = v; h }
+        [ctype, {"charset" => charset || defaults && defaults.charset}.merge(attrs)]
+      end
+
   end
 end
diff --git a/actionmailer/test/mail_service_test.rb b/actionmailer/test/mail_service_test.rb
index b60b1c1b8b..0689bf6728 100755
--- a/actionmailer/test/mail_service_test.rb
+++ b/actionmailer/test/mail_service_test.rb
@@ -246,6 +246,14 @@ class TestMailer < ActionMailer::Base
     body         "testing"
   end
 
+  def custom_content_type_attributes
+    recipients   "no.one@nowhere.test"
+    subject      "custom content types"
+    from         "some.one@somewhere.test"
+    content_type "text/plain; format=flowed"
+    body         "testing"
+  end
+
   class <<self
     attr_accessor :received_body
   end
@@ -787,5 +795,11 @@ EOF
     mail = FunkyPathMailer.create_multipart_with_template_path_with_dots(@recipient)
     assert_equal 2, mail.parts.length
   end
+
+  def test_custom_content_type_attributes
+    mail = TestMailer.create_custom_content_type_attributes
+    assert_match %r{format=flowed}, mail['content-type'].to_s
+    assert_match %r{charset=utf-8}, mail['content-type'].to_s
+  end
 end