diff --git a/app/models/custom_field.rb b/app/models/custom_field.rb
index 93e662785..7202076e8 100644
--- a/app/models/custom_field.rb
+++ b/app/models/custom_field.rb
@@ -16,6 +16,8 @@
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
 class CustomField < ActiveRecord::Base
+  include Redmine::SubclassFactory
+
   has_many :custom_values, :dependent => :delete_all
   acts_as_list :scope => 'type = \'#{self.class}\''
   serialize :possible_values
@@ -155,22 +157,6 @@ class CustomField < ActiveRecord::Base
     find(:all, :conditions => ["is_for_all=?", true], :order => 'position')
   end
 
-  # Returns an instance of the given subclass name
-  def self.new_subclass_instance(class_name, *args)
-    klass = nil
-    begin
-      klass = class_name.to_s.classify.constantize
-    rescue
-      # invalid class name
-    end
-    unless subclasses.include? klass
-      klass = nil
-    end
-    if klass
-      klass.new(*args)
-    end
-  end
-
   def type_name
     nil
   end
diff --git a/lib/redmine/subclass_factory.rb b/lib/redmine/subclass_factory.rb
new file mode 100644
index 000000000..9c223e3e9
--- /dev/null
+++ b/lib/redmine/subclass_factory.rb
@@ -0,0 +1,42 @@
+# Redmine - project management software
+# Copyright (C) 2006-2011  Jean-Philippe Lang
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+module Redmine
+  module SubclassFactory
+    def self.included(base) 
+      base.extend ClassMethods
+    end 
+
+    module ClassMethods
+      # Returns an instance of the given subclass name
+      def new_subclass_instance(class_name, *args)
+        klass = nil
+        begin
+          klass = class_name.to_s.classify.constantize
+        rescue
+          # invalid class name
+        end
+        unless subclasses.include? klass
+          klass = nil
+        end
+        if klass
+          klass.new(*args)
+        end
+      end
+    end
+  end
+end