diff --git a/ChangeLog b/ChangeLog
index 57909c5a7e..ad81cc15ae 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Nov 28 02:55:35 2012  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* configure.in (ARCH_FLAG): __sync_val_compare_and_swap_4 needs
+	  -march=i486 on at least linux gcc 4.1.
+
 Tue Nov 27 22:03:09 2012  Akinori MUSHA  <knu@iDaemons.org>
 
 	* string.c (rb_str_enumerate_chars, rb_str_enumerate_codepoints)
diff --git a/configure.in b/configure.in
index 7fa99c6d55..a543fe7f52 100644
--- a/configure.in
+++ b/configure.in
@@ -241,9 +241,10 @@ AC_ARG_WITH(arch,
 
 AC_DEFUN([RUBY_DEFAULT_ARCH], [
 AC_MSG_CHECKING([arch option])
-AS_CASE([$1],
-	[*64],        [ARCH_FLAG=-m64],
-	[[i[3-6]86]], [ARCH_FLAG=-m32],
+AS_CASE([$1-$target_os],
+	[*64-*],        [ARCH_FLAG=-m64],
+	[[i[3-6]86-linux]], [ARCH_FLAG=-march=i486],
+	[[i[3-6]86-*]], [ARCH_FLAG=-m32],
 	[AC_MSG_ERROR(unknown target architecture: $target_archs)]
 	)
 AC_MSG_RESULT([$ARCH_FLAG])