diff --git a/ChangeLog b/ChangeLog
index cf7d30b7d6..1c38396c11 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Oct 13 22:32:34 2010  Takeyuki FUJIOKA  <xibbar@ruby-lang.org>
+
+	* lib/cgi/util.rb (CGI::unescape): bugfix to unescape the multibyte
+	  string. Thanks nobu and tDiary dev members. [Bug #3909]
+
 Wed Oct 13 21:13:00 2010  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* numeric.c (int_chr): raise error when the value is negative.
diff --git a/lib/cgi/util.rb b/lib/cgi/util.rb
index 7be3e92577..9f8a63ac92 100644
--- a/lib/cgi/util.rb
+++ b/lib/cgi/util.rb
@@ -14,7 +14,7 @@ class CGI
   #   string = CGI::unescape("%27Stop%21%27+said+Fred")
   #      # => "'Stop!' said Fred"
   def CGI::unescape(string,encoding=@@accept_charset)
-    str=string.tr('+', ' ').gsub(/((?:%[0-9a-fA-F]{2})+)/) do
+    str=string.tr('+', ' ').force_encoding(Encoding::ASCII_8BIT).gsub(/((?:%[0-9a-fA-F]{2})+)/) do
       [$1.delete('%')].pack('H*')
     end.force_encoding(encoding)
     str.valid_encoding? ? str : str.force_encoding(string.encoding)
diff --git a/test/cgi/test_cgi_util.rb b/test/cgi/test_cgi_util.rb
index 479df68159..71e8beac3d 100644
--- a/test/cgi/test_cgi_util.rb
+++ b/test/cgi/test_cgi_util.rb
@@ -27,6 +27,7 @@ class CGIUtilTest < Test::Unit::TestCase
   def test_cgi_unescape
     assert_equal(@str1, CGI::unescape('%26%3C%3E%22+%E3%82%86%E3%82%93%E3%82%86%E3%82%93'))
     assert_equal(@str1.encoding, CGI::unescape('%26%3C%3E%22+%E3%82%86%E3%82%93%E3%82%86%E3%82%93').encoding) if defined?(::Encoding)
+    assert_equal("\u{30E1 30E2 30EA 691C 7D22}", CGI.unescape("\u{30E1 30E2 30EA}%E6%A4%9C%E7%B4%A2"))
   end
 
   def test_cgi_pretty