diff --git a/ChangeLog b/ChangeLog
index e4f3c29d5b..c1365ef5ba 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+Wed May 12 11:39:10 2010  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* ext/socket/extconf.rb: test all IPPROTO_* constants for recent Win32
+	  SDK.
+
+Tue May 11 23:07:22 2010  Tanaka Akira  <akr@fsij.org>
+
+	* ext/socket/extconf.rb: test IPPROTO_IP and IPPROTO_IPV6 constants.
+
+	* ext/socket/mkconstants.rb: define macros for enum.
+
+	  [ruby-dev:38849]
+
 Wed May 12 09:21:05 2010  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* re.c (rb_reg_initialize_m): fix wrong index for the lang
diff --git a/ext/socket/extconf.rb b/ext/socket/extconf.rb
index 3ce8316c4f..71deaa218d 100644
--- a/ext/socket/extconf.rb
+++ b/ext/socket/extconf.rb
@@ -110,6 +110,12 @@ end
 have_header("netinet/tcp.h") if /cygwin/ !~ RUBY_PLATFORM # for cygwin 1.1.5
 have_header("netinet/udp.h")
 
+if !have_macro("IPPROTO_IPV6", headers) && have_const("IPPROTO_IPV6", headers)
+  IO.read(File.join(File.dirname(__FILE__), "mkconstants.rb")).sub(/\A.*^__END__$/m, '').split(/\r?\n/).grep(/\AIPPROTO_\w*/){$&}.each {|name|
+    have_const(name, headers) unless $defs.include?("-DHAVE_CONST_#{name.upcase}")
+  }
+end
+
 if (have_func("sendmsg") | have_func("recvmsg")) && /64-darwin/ !~ RUBY_PLATFORM
   # CMSG_ macros are broken on 64bit darwin, because of use of __DARWIN_ALIGN.
   have_struct_member('struct msghdr', 'msg_control', ['sys/types.h', 'sys/socket.h'])
@@ -335,7 +341,7 @@ have_header("ucred.h", headers)
 have_func("getpeerucred")
 
 # workaround for recent Windows SDK
-$defs << "-DIPPROTO_IPV6=IPPROTO_IPV6" if have_const("IPPROTO_IPV6") && !have_macro("IPPROTO_IPV6")
+$defs << "-DIPPROTO_IPV6=IPPROTO_IPV6" if $defs.include?("-DHAVE_CONST_IPPROTO_IPV6") && !have_macro("IPPROTO_IPV6")
 
 $distcleanfiles << "constants.h" << "constdefs.*"
 
diff --git a/ext/socket/mkconstants.rb b/ext/socket/mkconstants.rb
index c796cb4870..fe00f30e3d 100644
--- a/ext/socket/mkconstants.rb
+++ b/ext/socket/mkconstants.rb
@@ -73,11 +73,15 @@ end
 
 ERB.new(<<'EOS', nil, '%').def_method(Object, "gen_const_decls")
 % each_const {|guard, make_value, name, default_value|
-%   if default_value
-#ifndef <%=name%>
-# define <%=name%> <%=default_value%>
+#if !defined(<%=name%>)
+# if defined(HAVE_CONST_<%=name.upcase%>)
+#  define <%=name%> <%=name%>
+%if default_value
+# else
+#  define <%=name%> <%=default_value%>
+%end
+# endif
 #endif
-%   end
 % }
 EOS