diff --git a/lib/fluent/command/fluentd.rb b/lib/fluent/command/fluentd.rb
index e66285bf81..2f08689b07 100644
--- a/lib/fluent/command/fluentd.rb
+++ b/lib/fluent/command/fluentd.rb
@@ -85,9 +85,8 @@
   opts[:log_path] = s
 }
 
-ROTATE_AGE = %w(daily weekly monthly)
 op.on('--log-rotate-age AGE', 'generations to keep rotated log files') {|age|
-  if ROTATE_AGE.include?(age)
+  if Fluent::Log::LOG_ROTATE_AGE.include?(age)
     opts[:log_rotate_age] = age
   else
     begin
diff --git a/lib/fluent/log.rb b/lib/fluent/log.rb
index 4c096a615e..201b2d88a6 100644
--- a/lib/fluent/log.rb
+++ b/lib/fluent/log.rb
@@ -49,6 +49,7 @@ module TTYColor
     LOG_TYPE_DEFAULT = :default # show logs in all supervisor/workers, with worker id in workers (default)
 
     LOG_TYPES = [LOG_TYPE_SUPERVISOR, LOG_TYPE_WORKER0, LOG_TYPE_DEFAULT].freeze
+    LOG_ROTATE_AGE = %w(daily weekly monthly)
 
     def self.str_to_level(log_level_str)
       case log_level_str.downcase
diff --git a/lib/fluent/system_config.rb b/lib/fluent/system_config.rb
index 746268854c..b322b4bb60 100644
--- a/lib/fluent/system_config.rb
+++ b/lib/fluent/system_config.rb
@@ -56,7 +56,7 @@ class SystemConfig
       config_param :format, :enum, list: [:text, :json], default: :text
       config_param :time_format, :string, default: '%Y-%m-%d %H:%M:%S %z'
       config_param :rotate_age, default: nil do |v|
-        if %w(daily weekly monthly).include?(v)
+        if Fluent::Log::LOG_ROTATE_AGE.include?(v)
           v.to_sym
         else
           begin