diff --git a/ChangeLog b/ChangeLog
index e9cd6782b3..aa89caf350 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Thu Sep 30 09:29:06 2010  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* lib/uri/common.rb (URI.encode_www_form): change treatment of
+	  undefined value in given array as latest internet draft for
+	  application/www-form-urlencoded.
+	  http://tools.ietf.org/html/draft-hoehrmann-urlencoded-01
+
 Thu Sep 30 09:34:03 2010  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* vm_dump.c (dump_thread): fixed wrong type of return value of
@@ -74,10 +81,10 @@ Mon Sep 27 23:30:34 2010  Koichi Sasada  <ko1@atdot.net>
 Mon Sep 27 15:54:03 2010  URABE Shyouhei  <shyouhei@ruby-lang.org>
 
 	* test/net/http/test_https.rb: As always, localhost is not
-          guaranteed to be resolved as 127.0.0.1.  But a SSL
-          certificate needs a socket to listen on a specific address
-          where a CN resolves to.  On situations where localhost is
-          not 127.0.0.1, these tests are not possible.
+	  guaranteed to be resolved as 127.0.0.1.  But a SSL
+	  certificate needs a socket to listen on a specific address
+	  where a CN resolves to.  On situations where localhost is
+	  not 127.0.0.1, these tests are not possible.
 
 Mon Sep 27 15:25:05 2010  URABE Shyouhei  <shyouhei@ruby-lang.org>
 
@@ -258,7 +265,7 @@ Sun Sep 19 20:37:45 2010  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
 
 	* Makefile.in (clean-capi, distclean-capi, realclean-capi): ditto.
 
-	* win32/Makefile.sub (clean-capi, distclean-capi, realclean-capi): 
+	* win32/Makefile.sub (clean-capi, distclean-capi, realclean-capi):
 	  ditto.
 
 Sun Sep 19 13:44:24 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
@@ -734,7 +741,7 @@ Sat Sep  4 10:40:50 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 Sun May 23 17:29:41 2010  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
 
-	* common.mk (capi): uses a timestamp file to get rid of 
+	* common.mk (capi): uses a timestamp file to get rid of
 	  generating twice.
 
 Fri Jun 18 01:33:21 2010  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
diff --git a/lib/uri/common.rb b/lib/uri/common.rb
index 3f92423b1a..e6f189bdbe 100644
--- a/lib/uri/common.rb
+++ b/lib/uri/common.rb
@@ -346,7 +346,7 @@ module URI
       ret[:REL_URI] = rel_uri = "(?:#{net_path}|#{abs_path}|#{rel_path})(?:\\?#{query})?"
 
       # URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ]
-      ret[:URI_REF] = uri_ref = "(?:#{abs_uri}|#{rel_uri})?(?:##{fragment})?"
+      ret[:URI_REF] = "(?:#{abs_uri}|#{rel_uri})?(?:##{fragment})?"
 
       ret[:X_ABS_URI] = "
         (#{scheme}):                           (?# 1: scheme)
@@ -797,18 +797,14 @@ module URI
   #
   # See URI.encode_www_form_component, URI.decode_www_form
   def self.encode_www_form(enum)
-    str = nil
-    enum.each do |k,v|
-      if str
-        str << '&'
-      else
-        str = nil.to_s
+    enum.map do |k,v|
+      str = encode_www_form_component(k)
+      if v
+        str << '='
+        str << encode_www_form_component(v)
       end
-      str << encode_www_form_component(k)
-      str << '='
-      str << encode_www_form_component(v)
-    end
-    str
+      str
+    end.join('&')
   end
 
   WFKV_ = '(?:%\h\h|[^%#=;&]+)' # :nodoc:
diff --git a/test/uri/test_common.rb b/test/uri/test_common.rb
index 01381b20e6..410f46bd0b 100644
--- a/test/uri/test_common.rb
+++ b/test/uri/test_common.rb
@@ -82,6 +82,21 @@ class TestCommon < Test::Unit::TestCase
     assert_equal(expected, URI.encode_www_form(a: 1, :"\u3042" => "\u6F22"))
     assert_equal(expected, URI.encode_www_form([["a", "1"], ["\u3042", "\u6F22"]]))
     assert_equal(expected, URI.encode_www_form([[:a, 1], [:"\u3042", "\u6F22"]]))
+
+    assert_equal('+a+=+1+', URI.encode_www_form([[' a ', ' 1 ']]))
+    assert_equal('text=x%0Ay', URI.encode_www_form([['text', "x\u000Ay"]]))
+    assert_equal('constellation=Bo%C3%B6tes', URI.encode_www_form([['constellation', "Bo\u00F6tes"]]))
+    assert_equal('name=%00value', URI.encode_www_form([['name', "\u0000value"]]))
+    assert_equal('Cipher=c%3D%28m%5Ee%29%25n', URI.encode_www_form([['Cipher', 'c=(m^e)%n']]))
+    assert_equal('&', URI.encode_www_form([['', nil], ['', nil]]))
+    assert_equal('&=', URI.encode_www_form([['', nil], ['', '']]))
+    assert_equal('=&', URI.encode_www_form([['', ''], ['', nil]]))
+    assert_equal('=&=', URI.encode_www_form([['', ''], ['', '']]))
+    assert_equal('', URI.encode_www_form([['', nil]]))
+    assert_equal('', URI.encode_www_form([]))
+    assert_equal('=', URI.encode_www_form([['', '']]))
+    assert_equal('a%26b=1&c=2%3B3&e=4', URI.encode_www_form([['a&b', '1'], ['c', '2;3'], ['e', '4']]))
+    assert_equal('image&title&price', URI.encode_www_form([['image', nil], ['title', nil], ['price', nil]]))
   end
 
   def test_decode_www_form