diff --git a/ChangeLog b/ChangeLog
index e9bd0e9bc1..f0904b6d2a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu May 31 17:27:53 2007  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/benchmark.rb (Benchmark::Job::item): avoid modifying the
+	  argument unintentionally.  [ruby-talk:253676]
+
 Wed May 30 14:43:00 2007  Koichi Sasada  <ko1@atdot.net>
 
 	* cont.c (cont_capture): store all local variables in heap
diff --git a/lib/benchmark.rb b/lib/benchmark.rb
index 36e593518f..c7c3935131 100644
--- a/lib/benchmark.rb
+++ b/lib/benchmark.rb
@@ -331,7 +331,7 @@ module Benchmark
     #
     def item(label = "", &blk) # :yield:
       raise ArgmentError, "no block" unless block_given?
-      label.concat ' '
+      label += ' '
       w = label.length
       @width = w if @width < w
       @list.push [label, blk]
diff --git a/version.h b/version.h
index 3ab78c0e4f..90d0eb27ab 100644
--- a/version.h
+++ b/version.h
@@ -1,7 +1,7 @@
 #define RUBY_VERSION "1.9.0"
-#define RUBY_RELEASE_DATE "2007-05-30"
+#define RUBY_RELEASE_DATE "2007-05-31"
 #define RUBY_VERSION_CODE 190
-#define RUBY_RELEASE_CODE 20070530
+#define RUBY_RELEASE_CODE 20070531
 #define RUBY_PATCHLEVEL 0
 
 #define RUBY_VERSION_MAJOR 1
@@ -9,7 +9,7 @@
 #define RUBY_VERSION_TEENY 0
 #define RUBY_RELEASE_YEAR 2007
 #define RUBY_RELEASE_MONTH 5
-#define RUBY_RELEASE_DAY 30
+#define RUBY_RELEASE_DAY 31
 
 #ifdef RUBY_EXTERN
 RUBY_EXTERN const char ruby_version[];