diff --git a/ChangeLog b/ChangeLog
index 180ccd1d27..82eba1f742 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Wed Aug 12 21:07:46 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* ext/socket/extconf.rb: if ipv6 is enabled, the version of Windows
+	  most be XP or later.
+	  [ruby-core:24601]
+
 Wed Aug 12 15:59:29 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* common.mk (yes-test-knownbug): use RUNRUBY instead of MINIRUBY.
diff --git a/ext/socket/extconf.rb b/ext/socket/extconf.rb
index 21f99b9848..1d233fdd1f 100644
--- a/ext/socket/extconf.rb
+++ b/ext/socket/extconf.rb
@@ -52,6 +52,9 @@ EOF
 end
 
 if ipv6
+  if $mingw
+    $CPPFLAGS << " -D_WIN32_WINNT=0x501"
+  end
   ipv6lib = nil
   class << (fmt = "unknown")
     def %(s) s || self end