diff --git a/ChangeLog b/ChangeLog
index e7ec941819..1a53aea298 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Nov  8 05:31:25 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* safe.c (safe_setter): add warning for $SAFE=3.
+
 Sat Nov  8 01:48:07 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* thread_pthread.c (rb_thread_create_timer_thread): do not wait never
diff --git a/safe.c b/safe.c
index e351579132..ebe62f4206 100644
--- a/safe.c
+++ b/safe.c
@@ -66,6 +66,9 @@ safe_setter(VALUE val)
 		 "tried to downgrade safe level from %d to %d",
 		 th->safe_level, level);
     }
+    if (level == 3) {
+	rb_warning("$SAFE=3 does no sandboxing; you might want to use $SAFE=4");
+    }
     if (level > SAFE_LEVEL_MAX) {
 	level = SAFE_LEVEL_MAX;
     }