diff --git a/README.md b/README.md
index 2c8a055..0b50d72 100644
--- a/README.md
+++ b/README.md
@@ -33,4 +33,4 @@ You can setup options in administration menu.
 
 ## Compatibility
 
-This version supports redmine 3.x.
+This version supports redmine 4.x.
diff --git a/app/controllers/reminder_configuration_controller.rb b/app/controllers/reminder_configuration_controller.rb
index ab289b0..8bf8845 100644
--- a/app/controllers/reminder_configuration_controller.rb
+++ b/app/controllers/reminder_configuration_controller.rb
@@ -3,7 +3,7 @@ class ReminderConfigurationController < ApplicationController
 
   layout 'admin'
 
-  before_filter :require_admin
+  before_action :require_admin
 
   def edit
     @configuration = ReminderConfiguration.instance
diff --git a/init.rb b/init.rb
index e243884..7f12d33 100644
--- a/init.rb
+++ b/init.rb
@@ -14,4 +14,4 @@
     html: { class: 'reminder_options_label' }
 end
 
-require_dependency 'redmine_reminder/hooks'
+require File.expand_path('lib/hooks', __dir__)
diff --git a/lib/ar_condition.rb b/lib/ar_condition.rb
index efd6989..07d6b46 100644
--- a/lib/ar_condition.rb
+++ b/lib/ar_condition.rb
@@ -15,7 +15,7 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
-class ARCondition
+class ArCondition
   attr_reader :conditions
   
   def initialize(condition=nil)
diff --git a/lib/redmine_reminder/collector.rb b/lib/collector.rb
similarity index 96%
rename from lib/redmine_reminder/collector.rb
rename to lib/collector.rb
index 90ed49c..0fe8a2f 100644
--- a/lib/redmine_reminder/collector.rb
+++ b/lib/collector.rb
@@ -1,4 +1,4 @@
-class RedmineReminder::Collector
+class Collector
   attr_reader :options
 
   def initialize(options)
@@ -48,7 +48,7 @@ def collect_reminders
   # Get issues due in X days
   def issues_due_in_days
     due_date      = options.days.day.from_now.to_date
-    sql_condition = ARCondition.new ["#{Issue.table_name}.due_date <= ?", due_date]
+    sql_condition = ArCondition.new ["#{Issue.table_name}.due_date <= ?", due_date]
     sql_condition << issue_statuses
     sql_condition << projects
     sql_condition << trackers
diff --git a/lib/hooks.rb b/lib/hooks.rb
new file mode 100644
index 0000000..48d9e50
--- /dev/null
+++ b/lib/hooks.rb
@@ -0,0 +1,5 @@
+class Hooks < Redmine::Hook::ViewListener
+  render_on :view_layouts_base_html_head,
+    partial: 'hooks/redmine_reminder/includes'
+end
+
diff --git a/lib/redmine_reminder/hooks.rb b/lib/redmine_reminder/hooks.rb
deleted file mode 100644
index 53c6588..0000000
--- a/lib/redmine_reminder/hooks.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-module RedmineReminder
-  class Hooks < Redmine::Hook::ViewListener
-    render_on :view_layouts_base_html_head,
-      partial: 'hooks/redmine_reminder/includes'
-  end
-end
-
diff --git a/lib/redmine_reminder/reminder.rb b/lib/reminder.rb
similarity index 89%
rename from lib/redmine_reminder/reminder.rb
rename to lib/reminder.rb
index 5c2a30a..955b7fa 100644
--- a/lib/redmine_reminder/reminder.rb
+++ b/lib/reminder.rb
@@ -1,4 +1,4 @@
-class RedmineReminder::Reminder
+class Reminder
   attr_reader :user, :issues
 
   def initialize(user)