diff --git a/ChangeLog b/ChangeLog
index 1d84a2044e..936c8b77f9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat May 10 08:47:36 2014  Tanaka Akira  <akr@fsij.org>
+
+	* signal.c (trap): Return "SYSTEM_DEFAULT" if SIG_DFL is set.
+
 Fri May  9 14:27:05 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* configure.in (RUBY_SETJMP_TYPE): check for setjmp type after
diff --git a/signal.c b/signal.c
index 8625d942d4..7dc4247220 100644
--- a/signal.c
+++ b/signal.c
@@ -976,6 +976,7 @@ trap(int sig, sighandler_t func, VALUE command)
     switch (oldcmd) {
       case 0:
 	if (oldfunc == SIG_IGN) oldcmd = rb_str_new2("IGNORE");
+        else if (oldfunc == SIG_DFL) oldcmd = rb_str_new2("SYSTEM_DEFAULT");
 	else if (oldfunc == sighandler) oldcmd = rb_str_new2("DEFAULT");
 	else oldcmd = Qnil;
 	break;
diff --git a/test/ruby/test_signal.rb b/test/ruby/test_signal.rb
index 14be2d76aa..68da0d5840 100644
--- a/test/ruby/test_signal.rb
+++ b/test/ruby/test_signal.rb
@@ -175,6 +175,13 @@ class TestSignal < Test::Unit::TestCase
     end;
   end if Process.respond_to?(:kill)
 
+  def test_trap_system_default
+    assert_separately([], <<-End)
+      trap(:QUIT, "SYSTEM_DEFAULT")
+      assert_equal("SYSTEM_DEFAULT", trap(:QUIT, "DEFAULT"))
+    End
+  end
+
   def test_signal_requiring
     t = Tempfile.new(%w"require_ensure_test .rb")
     t.puts "sleep"