diff -uNpr redmine-2.5.1-orig/lib/redmine/mime_type.rb redmine-2.5.1/lib/redmine/mime_type.rb
--- redmine-2.5.1-orig/lib/redmine/mime_type.rb	2014-03-29 17:56:41.000000000 +0100
+++ redmine-2.5.1/lib/redmine/mime_type.rb	2014-04-17 13:39:18.407305449 +0200
@@ -60,7 +60,7 @@ module Redmine
         extension = m[2].downcase
         @known_types ||= Hash.new do |h, ext|
           type = EXTENSIONS[ext]
-          type ||= MIME::Types.find {|type| type.extensions.include?(ext)}.to_s.presence
+          type ||= MIME::Types.type_for(ext).first.to_s.presence
           h[ext] = type
         end
         @known_types[extension]