diff --git a/app/models/dmsf_folder.rb b/app/models/dmsf_folder.rb
index 6af5feed..1e196386 100644
--- a/app/models/dmsf_folder.rb
+++ b/app/models/dmsf_folder.rb
@@ -96,6 +96,7 @@ class DmsfFolder < ActiveRecord::Base
   validates_uniqueness_of :title, scope: [:dmsf_folder_id, :project_id, :deleted],
     conditions: -> { where(deleted: STATUS_ACTIVE) }
   validates :description, length: { maximum: 65535 }
+  validates :dmsf_folder, dmsf_folder_parent: true, if: Proc.new { |folder| !folder.new_record? }
 
   before_create :default_values
 
diff --git a/app/validators/dmsf_folder_parent_validator.rb b/app/validators/dmsf_folder_parent_validator.rb
new file mode 100644
index 00000000..747e4087
--- /dev/null
+++ b/app/validators/dmsf_folder_parent_validator.rb
@@ -0,0 +1,37 @@
+# encoding: utf-8
+# frozen_string_literal: true
+#
+# Redmine plugin for Document Management System "Features"
+#
+# Copyright © 2011-20 Karel Pičman <karel.picman@kontron.com>
+#
+# 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.
+
+class DmsfFolderParentValidator  < ActiveModel::EachValidator
+
+  # Don't allow save folders with a parent pointing to the same folder
+  def validate_each(record, attribute, value)
+    folder = value
+    while folder
+      if folder == record
+        record.errors.add attribute, :invalid
+        return false
+      end
+      folder = folder.dmsf_folder
+    end
+    return true
+  end
+
+end
\ No newline at end of file
diff --git a/lib/redmine_dmsf.rb b/lib/redmine_dmsf.rb
index d0fac574..4c05e632 100644
--- a/lib/redmine_dmsf.rb
+++ b/lib/redmine_dmsf.rb
@@ -29,6 +29,7 @@ DMSF_MAX_NOTIFICATION_RECEIVERS_INFO = 10
 require_dependency File.dirname(__FILE__) + '/../app/validators/dmsf_file_name_validator'
 require_dependency File.dirname(__FILE__) + '/../app/validators/dmsf_workflow_name_validator'
 require_dependency File.dirname(__FILE__) + '/../app/validators/dmsf_url_validator'
+require_dependency File.dirname(__FILE__) + '/../app/validators/dmsf_folder_parent_validator'
 
 # Plugin's patches
 require 'redmine_dmsf/patches/projects_helper_patch'
diff --git a/test/unit/dmsf_folder_test.rb b/test/unit/dmsf_folder_test.rb
index a9067216..c7eaa62b 100644
--- a/test/unit/dmsf_folder_test.rb
+++ b/test/unit/dmsf_folder_test.rb
@@ -237,4 +237,20 @@ class DmsfFolderTest < RedmineDmsf::Test::UnitTest
     assert DmsfFolder.find_by(project_id: @project2.id, title: @folder1.title)
   end
 
+  def test_valid_parent
+    @folder2.dmsf_folder = @folder1
+    assert @folder2.save
+  end
+
+  def test_valid_parent_nil
+    @folder2.dmsf_folder = nil
+    assert @folder2.save
+  end
+
+  def test_valid_parent_loop
+    @folder1.dmsf_folder = @folder2
+    # @folder2 is under @folder1 => loop!
+    assert !@folder1.save
+  end
+
 end
\ No newline at end of file