diff --git a/ChangeLog b/ChangeLog
index e5f6a69929..fecfe9650e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Mar 29 11:09:48 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/mkmf.rb (configuration): not include all CFLAGS in CXXFLAGS, to
+	  use different set than C for C++.  [ruby-core:45273] [Bug #6504]
+
 Fri Mar 29 10:24:10 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* include/ruby/io.h: undef POSIX compliants names on AIX, which are no
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 0fd930b47c..90d28ab449 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -1863,11 +1863,12 @@ cflags   = #{CONFIG['cflags']}
 optflags = #{CONFIG['optflags']}
 debugflags = #{CONFIG['debugflags']}
 warnflags = #{$warnflags}
-CFLAGS   = #{$static ? '' : CONFIG['CCDLFLAGS']} #$CFLAGS $(ARCH_FLAG)
+CCDLFLAGS = #{$static ? '' : CONFIG['CCDLFLAGS']}
+CFLAGS   = $(CCDLFLAGS) #$CFLAGS $(ARCH_FLAG)
 INCFLAGS = -I. #$INCFLAGS
 DEFS     = #{CONFIG['DEFS']}
 CPPFLAGS = #{extconf_h}#{$CPPFLAGS}
-CXXFLAGS = $(CFLAGS) #{CONFIG['CXXFLAGS']}
+CXXFLAGS = $(CCDLFLAGS) #{CONFIG['CXXFLAGS']} $(ARCH_FLAG)
 ldflags  = #{$LDFLAGS}
 dldflags = #{$DLDFLAGS} #{CONFIG['EXTDLDFLAGS']}
 ARCH_FLAG = #{$ARCH_FLAG}