diff --git a/ChangeLog b/ChangeLog
index d379ca74f6..b5a605bb5d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Feb  8 23:25:33 2013  Tanaka Akira  <akr@fsij.org>
+
+	* configure.in: change CFLAGS temporally to test
+	  ARCH_FLAG="-march=i486".
+
 Fri Feb  8 21:19:41 2013  Tanaka Akira  <akr@fsij.org>
 
 	* configure.in: don't define ARCH_FLAG="-march=i486" if it causes
diff --git a/configure.in b/configure.in
index ea57241230..e3b57d4b94 100644
--- a/configure.in
+++ b/configure.in
@@ -1555,13 +1555,17 @@ AS_CASE(["$target_cpu-$target_os"], [[i[3-6]86*]], [
 	 if test "$rb_cv_gcc_compiler_cas" = no; then
 		 unset rb_cv_gcc_compiler_cas
 		 ARCH_FLAG="-march=i486"
+		 save_CFLAGS="$CFLAGS"
+		 CFLAGS="$CFLAGS -march=i486"
 		 AC_CACHE_CHECK([for __sync_val_compare_and_swap with -march=i486], [rb_cv_gcc_compiler_cas], [
 				 AC_TRY_LINK([unsigned long atomic_var;],
 					     [
 					      __sync_val_compare_and_swap(&atomic_var, 0, 1);
 					      ],
-					      [rb_cv_gcc_compiler_cas=yes],
-					      [rb_cv_gcc_compiler_cas=no; unset ARCH_FLAG])])
+					      [rb_cv_gcc_compiler_cas=yes
+					       ARCH_FLAG="-march=i486"],
+					      [rb_cv_gcc_compiler_cas=no])])
+		 CFLAGS="$save_CFLAGS"
 	 fi])
 
 AC_CACHE_CHECK(for signbit, rb_cv_have_signbit,