diff --git a/ChangeLog b/ChangeLog
index ad904455ec..1cf6939da2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri May 18 18:13:44 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/mkmf.rb (MakeMakefile#configuration): keep space at end of
+	  OUTFLAG and COUTFLAG.  [ruby-dev:45650]
+
 Fri May 18 17:39:42 2012  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* thread_pthread.c (rb_thread_create_timer_thread): Added error
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index d378d50fbd..1430aa30ef 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -1770,8 +1770,9 @@ LIBRUBY = #{CONFIG['LIBRUBY']}
 LIBRUBY_A = #{CONFIG['LIBRUBY_A']}
 LIBRUBYARG_SHARED = #$LIBRUBYARG_SHARED
 LIBRUBYARG_STATIC = #$LIBRUBYARG_STATIC
-OUTFLAG = #{OUTFLAG}
-COUTFLAG = #{COUTFLAG}
+empty =
+OUTFLAG = #{OUTFLAG}$(empty)
+COUTFLAG = #{COUTFLAG}$(empty)
 
 RUBY_EXTCONF_H = #{$extconf_h}
 cflags   = #{CONFIG['cflags']}