diff --git a/ChangeLog b/ChangeLog
index 4a34b0f289..dd100cf8a4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon May 16 11:21:09 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* configure.in, win32/Makefile.sub (RUBY_SO_NAME): add CPU as prefix
+	  of RUBY_SO_NAME on x64/ia64 mswin/mingw.
+
 Mon May 16 08:00:05 2011  Eric Hodel  <drbrain@segment7.net>
 
 	* lib/rdoc.rb:  Update to RDoc 3.6.1, allows OpenSSL::Digest to be
diff --git a/configure.in b/configure.in
index c29f2ee310..0d3d048a76 100644
--- a/configure.in
+++ b/configure.in
@@ -2472,6 +2472,9 @@ AS_CASE(["$target_os"],
 	    ],
 	[mingw*], [
 	    RUBY_SO_NAME="${rb_cv_msvcrt}-${RUBY_SO_NAME}"
+	    if test x"${target_cpu}" != xi386; then
+		RUBY_SO_NAME="${target_cpu}-${RUBY_SO_NAME}"
+	    fi
 	    if test x"$enable_shared" = xyes; then
 		LIBRUBY_SO='$(RUBY_SO_NAME)'.dll
 		LIBRUBY_DLDFLAGS="${LIBRUBY_DLDFLAGS}"' $(RUBYDEF)'
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index 4dd7b7993e..0b1361a7c1 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -130,6 +130,9 @@ ruby_version = $(MAJOR).$(MINOR).$(TEENY)
 
 !ifndef RUBY_SO_NAME
 RUBY_SO_NAME = $(RT)-$(RUBY_BASE_NAME)$(MAJOR)$(MINOR)$(TEENY)
+!if "$(ARCH)" != "i386"
+RUBY_SO_NAME = $(ARCH)-$(RUBY_SO_NAME)
+!endif
 !endif
 !ifndef RUBY_PLATFORM
 RUBY_PLATFORM = $(arch)