diff --git a/app/models/dmsf_file.rb b/app/models/dmsf_file.rb
index 57ca55bc..3b8f4695 100644
--- a/app/models/dmsf_file.rb
+++ b/app/models/dmsf_file.rb
@@ -20,6 +20,7 @@
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
 require 'xapian'
+require "#{File.dirname(__FILE__)}/../../lib/redmine_dmsf/lockable"
 
 # File
 class DmsfFile < ApplicationRecord
diff --git a/app/models/dmsf_folder.rb b/app/models/dmsf_folder.rb
index ee09beba..d9ee9da8 100644
--- a/app/models/dmsf_folder.rb
+++ b/app/models/dmsf_folder.rb
@@ -19,6 +19,8 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
+require "#{File.dirname(__FILE__)}/../../lib/redmine_dmsf/lockable"
+
 # Folder
 class DmsfFolder < ApplicationRecord
   include RedmineDmsf::Lockable