diff --git a/ChangeLog b/ChangeLog
index 4a9d305339..f1dd0aec1f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Mar  9 00:07:03 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/logger.rb (Logger::LogDevice#initialize): define using
+	  keyword arguments.
+
 Tue Mar  8 23:37:07 2016  Charles Oliver Nutter  <headius@headius.com>
 
 	* test/ruby/test_array.rb: split out the test for no stack error
diff --git a/lib/logger.rb b/lib/logger.rb
index 5a310bacb5..8393806a11 100644
--- a/lib/logger.rb
+++ b/lib/logger.rb
@@ -629,13 +629,13 @@ private
     attr_reader :filename
     include MonitorMixin
 
-    def initialize(log = nil, opt = {})
+    def initialize(log = nil, shift_age: nil, shift_size: nil)
       @dev = @filename = @shift_age = @shift_size = nil
       mon_initialize
       set_dev(log)
       if @filename
-        @shift_age = opt[:shift_age] || 7
-        @shift_size = opt[:shift_size] || 1048576
+        @shift_age = shift_age || 7
+        @shift_size = shift_size || 1048576
         @next_rotate_time = next_rotate_time(Time.now, @shift_age) unless @shift_age.is_a?(Integer)
       end
     end