diff --git a/ChangeLog b/ChangeLog
index a8d18620bf..7189f39344 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Tue Jul 12 11:58:28 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* win32/setup.mak: support x86-amd64 cross compile environment.
+
 Mon Jul 11 23:22:28 2011  Yutaka Kanemoto  <kanemoto@ruby-lang.org>
 
 	* time.c: can't compile time.c on AIX due to missing declaration for
diff --git a/win32/setup.mak b/win32/setup.mak
index 0733e99bbb..0d9990ae8e 100644
--- a/win32/setup.mak
+++ b/win32/setup.mak
@@ -204,6 +204,16 @@ RUBY_SO_NAME = $(RUBY_SO_NAME)
 $(ARCH) = x64
 !elseif "$(PROCESSOR_ARCHITECTURE)" == "IA64"
 $(ARCH) = ia64
+!elseif defined(PROCESSOR_ARCHITEW6432)
+$(BANG)if "$$(TARGET_OS)" == "mswin64"
+!if "$(PROCESSOR_ARCHITECTURE)" == "IA64"
+$(ARCH) = ia64
+!else
+$(ARCH) = x64
+!endif
+$(BANG)else
+$(ARCH) = $(PROCESSOR_ARCHITECTURE)
+$(BANG)endif
 !else
 $(ARCH) = $(PROCESSOR_ARCHITECTURE)
 !endif