diff --git a/ChangeLog b/ChangeLog
index 9334799874..80e85bfae3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+Mon Nov 22 14:13:45 2010  Masaki Suketa <masaki.suketa@nifty.ne.jp>
+
+	* ext/win32ole/win32ole.c: fix checking version of GCC.
+
+Mon Nov 22 14:13:45 2010  Masaki Suketa <masaki.suketa@nifty.ne.jp>
+
+	* ext/win32ole/win32ole.c: NONAMELESSUNION defined only if gcc
+	  version is older than 3.4.4. [ruby-core:31567] [Bug #3637]
+	* ext/win32ole/extconf.rb: ditto.
+
 Wed Nov 17 18:28:27 2010  Akinori MUSHA  <knu@iDaemons.org>
 
 	* array.c (rb_ary_sort_by_bang): Add Array#sort_by!.
diff --git a/ext/win32ole/extconf.rb b/ext/win32ole/extconf.rb
index ed6bf83cfa..aaa2d7c32c 100644
--- a/ext/win32ole/extconf.rb
+++ b/ext/win32ole/extconf.rb
@@ -35,7 +35,5 @@ end
 case RUBY_PLATFORM
 when /mswin32/
   $CFLAGS += ' /W3'
-when /cygwin/, /mingw/
-  $defs << '-DNONAMELESSUNION'
 end
 create_win32ole_makefile
diff --git a/ext/win32ole/win32ole.c b/ext/win32ole/win32ole.c
index b2c94eb92e..1f605a500e 100644
--- a/ext/win32ole/win32ole.c
+++ b/ext/win32ole/win32ole.c
@@ -17,6 +17,20 @@
 
 #include "ruby.h"
 #include "st.h"
+
+#define GNUC_OLDER_3_4_4 \
+    ((__GNUC__ < 3) || \
+     ((__GNUC__ <= 3) && (__GNUC_MINOR__ < 4)) || \
+     ((__GNUC__ <= 3) && (__GNUC_MINOR__ <= 4) && (__GNUC_PATCHLEVEL__ <= 4)))
+
+#if (defined(__GNUC__)) && (GNUC_OLDER_3_4_4) 
+#ifndef NONAMELESSUNION
+#define NONAMELESSUNION 1
+#endif
+#endif
+
+#include <ctype.h>
+
 #include <windows.h>
 #include <ocidl.h>
 #include <olectl.h>
@@ -37,13 +51,13 @@
 #define DOUTI(x) fprintf(stderr, "[%ld]:" #x "=%d\n",__LINE__,x)
 #define DOUTD(x) fprintf(stderr, "[%d]:" #x "=%f\n",__LINE__,x)
 
-#if defined NONAMELESSUNION && __GNUC__
+#if (defined(__GNUC__)) && (GNUC_OLDER_3_4_4) 
 #define V_UNION1(X, Y) ((X)->u.Y)
 #else
 #define V_UNION1(X, Y) ((X)->Y)
 #endif
 
-#if defined NONAMELESSUNION && __GNUC__
+#if (defined(__GNUC__)) && (GNUC_OLDER_3_4_4) 
 #undef V_UNION
 #define V_UNION(X,Y) ((X)->n1.n2.n3.Y)