diff --git a/ChangeLog b/ChangeLog
index 624a6bca93..7f9eb34561 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Jul 27 17:58:12 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* configure.in (RUBY_CPPOUTFILE): get rid of variable conflict so
+	  CPPFLAGS is not duplicated.  [ruby-core:43097] [Bug #6119]
+
 Fri Jul 27 12:12:36 2012  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* win32/mkexports.rb: should not export DllMain().
diff --git a/configure.in b/configure.in
index e2a158e1f5..3bb58b3d39 100644
--- a/configure.in
+++ b/configure.in
@@ -136,12 +136,12 @@ AC_DEFUN([RUBY_NACL_CHECK_PEPPER_TYPES],
 
 AC_DEFUN([RUBY_CPPOUTFILE],
 [AC_CACHE_CHECK(whether ${CPP} accepts -o, rb_cv_cppoutfile,
-[cppflags=$CPPFLAGS
+[save_CPPFLAGS="$CPPFLAGS"
 CPPFLAGS='-o conftest-1.i'
 rb_cv_cppoutfile=no
 AC_TRY_CPP([test-for-cppout],
 	   [grep test-for-cppout conftest-1.i > /dev/null && rb_cv_cppoutfile=yes])
-CPPFLAGS=$cppflags
+CPPFLAGS="$save_CPPFLAGS"
 rm -f conftest*])
 if test "$rb_cv_cppoutfile" = yes; then
   CPPOUTFILE='-o conftest.i'