diff --git a/ChangeLog b/ChangeLog
index decb68b4af..2d4334b394 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Jun  4 04:14:53 2001  Wakou Aoyama  <wakou@fsinet.or.jp>
+
+	* lib/shellwords.rb: don't destroy argument.
+
 Sat Jun  2 23:05:20 2001  Shugo Maeda <shugo@ruby-lang.org>
 
 	* lib/cgi/session.rb: don't use module_function for Class.
diff --git a/lib/shellwords.rb b/lib/shellwords.rb
index 5c31f8ca78..9fd7571172 100644
--- a/lib/shellwords.rb
+++ b/lib/shellwords.rb
@@ -16,7 +16,7 @@ module Shellwords
     unless line.kind_of?(String)
       raise ArgumentError, "Argument must be String class object."
     end
-    line.sub!(/\A\s+/, '')
+    line = line.sub(/\A\s+/, '')
     words = []
     while line != ''
       field = ''