diff --git a/ChangeLog b/ChangeLog
index 90f4d8232d..ab1b39d4a8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Dec  8 12:57:50 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* ext/socket/extconf.rb: forgotten to define HAVE_SOCKETPAIR for
+	  windows.
+
 Thu Dec  8 12:11:06 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* configure.in (RUBY_WERROR_FLAG): append all warning flags which
diff --git a/ext/socket/extconf.rb b/ext/socket/extconf.rb
index ba180c820e..2e308fe1ab 100644
--- a/ext/socket/extconf.rb
+++ b/ext/socket/extconf.rb
@@ -485,6 +485,7 @@ if have_func(test_func)
   have_func("getipnodebyname") or have_func("gethostbyname2")
   if !have_func("socketpair(0, 0, 0, 0)") and have_func("rb_w32_socketpair(0, 0, 0, 0)")
     $defs << "-Dsocketpair(a,b,c,d)=rb_w32_socketpair((a),(b),(c),(d))"
+    $defs << "-DHAVE_SOCKETPAIR"
   end
   unless have_func("gethostname((char *)0, 0)")
     have_func("uname")