diff --git a/ChangeLog b/ChangeLog
index 43838901de..93ffa9faaf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jan  2 14:55:28 2012  Kazuhiro NISHIYAMA  <zn@mbf.nifty.com>
+
+	* lib/test/unit.rb (Test::Unit::Runner#_run_parallel): find may
+	  return nil and nil can not dup.
+
 Sun Jan  1 12:23:10 2012  Akinori MUSHA  <knu@iDaemons.org>
 
 	* lib/shellwords.rb (Shellwords#shellescape): Drop the //n flag
diff --git a/lib/test/unit.rb b/lib/test/unit.rb
index 00313a3237..1bee643c31 100644
--- a/lib/test/unit.rb
+++ b/lib/test/unit.rb
@@ -433,8 +433,9 @@ module Test
             while stat = Process.wait2
               break if @interrupt # Break when interrupt
               pid, stat = stat
-              w = (@workers + @dead_workers).find{|x| pid == x.pid }.dup
+              w = (@workers + @dead_workers).find{|x| pid == x.pid }
               next unless w
+              w = w.dup
               if w.status != :quit && !w.quit_called?
                 # Worker down
                 w.died(nil, !stat.signaled? && stat.exitstatus)