diff --git a/ChangeLog b/ChangeLog
index 33372b3eab..27e9d3bc1a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Nov  4 10:30:40 2010  URABE Shyouhei  <shyouhei@ruby-lang.org>
+
+	* configure.in (--with-valgrind): Now this option is default on.
+	  You can still explicitly disable this feature by specifying
+	  --without-valgrind.
+
 Thu Nov  4 02:06:16 2010  Yusuke Endoh  <mame@tsg.ne.jp>
 
 	* cont.c (fiber_t_alloc): raise an error when fiber is going to be
diff --git a/configure.in b/configure.in
index b85b3421bd..7dd61776b4 100644
--- a/configure.in
+++ b/configure.in
@@ -1781,6 +1781,8 @@ AC_CHECK_FUNCS(backtrace)
 
 AC_ARG_WITH(valgrind,
         AS_HELP_STRING([--with-valgrind],[enable valgrind memcheck support]),
+        ruby_cv_with_valgrind=yes,ruby_cv_with_valgrind=no)
+AS_IF([test x$ruby_cv_with_valgrind != xno],
         [AC_CHECK_HEADERS(valgrind/memcheck.h)])
 
 dnl }