diff --git a/app/models/attachment.rb b/app/models/attachment.rb
index 0cd666499..0b151dabb 100644
--- a/app/models/attachment.rb
+++ b/app/models/attachment.rb
@@ -245,7 +245,7 @@ class Attachment < ActiveRecord::Base
   end
 
   def is_textile?
-    self.filename =~ /\.textile$/i
+    Redmine::MimeType.of(filename) == 'text/x-textile'
   end
 
   def is_image?
diff --git a/lib/redmine/mime_type.rb b/lib/redmine/mime_type.rb
index e4801da21..23bd3df1d 100644
--- a/lib/redmine/mime_type.rb
+++ b/lib/redmine/mime_type.rb
@@ -35,6 +35,7 @@ module Redmine
       'text/x-ruby' => 'rb,rbw,ruby,rake,erb',
       'text/x-csh' => 'csh',
       'text/x-sh' => 'sh',
+      'text/x-textile' => 'textile',
       'text/xml' => 'xml,xsd,mxml',
       'text/yaml' => 'yml,yaml',
       'text/csv' => 'csv',