diff --git a/ChangeLog b/ChangeLog
index 6fd1eb90ce..0759cbb454 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Sep 11 21:38:13 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* tool/config.{guess,sub}: better guess on darwin 10 .
+
 Fri Sep 11 18:51:57 2009  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* test/fileutils: use require_relative to require fileasserts.
diff --git a/configure.in b/configure.in
index 973256a142..98c08d7c4e 100644
--- a/configure.in
+++ b/configure.in
@@ -202,6 +202,29 @@ if test ${target_archs+set}; then
     CFLAGS="$CFLAGS ${ARCH_FLAG}"
     LDFLAGS="${LDFLAGS+$LDFLAGS }${ARCH_FLAG}"
 else
+    if test x"$target_alias" = x; then
+	case "$target_os" in
+	  when(darwin*)
+	    AC_MSG_CHECKING([for real target cpu])
+	    target_cpu=`$CC -E - 2>/dev/null <<EOF |
+#ifdef __x86_64__
+"processor-name=x86_64"
+#endif
+#ifdef __i386__
+"processor-name=i386"
+#endif
+#ifdef __ppc__
+"processor-name=powerpc"
+#endif
+#ifdef __ppc64__
+"processor-name=powerpc64"
+#endif
+EOF
+	    sed -n 's/^"processor-name=\(.*\)"/\1/p'`
+	    AC_MSG_RESULT([$target_cpu])
+	    ;;
+	esac
+    fi
     target_archs="$target_cpu"
 fi