diff --git a/ChangeLog b/ChangeLog
index 61d571158d..6be574db11 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Nov 14 21:44:56 2015  Tanaka Akira  <akr@fsij.org>
+
+	* lib/time.rb: Use "<<" to reduce string allocation.
+
 Sat Nov 14 17:45:49 2015  Tanaka Akira  <akr@fsij.org>
 
 	* lib/tsort.rb: Specify frozen_string_literal: true.
diff --git a/lib/time.rb b/lib/time.rb
index 2ab069509c..69e524fd61 100644
--- a/lib/time.rb
+++ b/lib/time.rb
@@ -616,7 +616,7 @@ class Time
     sprintf('%s, %02d %s %0*d %02d:%02d:%02d ',
       RFC2822_DAY_NAME[wday],
       day, RFC2822_MONTH_NAME[mon-1], year < 0 ? 5 : 4, year,
-      hour, min, sec) +
+      hour, min, sec) <<
     if utc?
       '-0000'
     else