diff --git a/ChangeLog b/ChangeLog
index 2ae051a215..8e85676791 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Mar  2 13:04:27 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* signal.c (sig_signame): return nil if the argument is a valid
+	  signal number.
+
 Mon Mar  2 12:05:04 2015  Naohisa Goto  <ngotogenome@gmail.com>
 
 	* test/net/ftp/test_ftp.rb (create_ftp_server): set SO_OOBINLINE
diff --git a/signal.c b/signal.c
index fcfed8d42e..53e77d9ca4 100644
--- a/signal.c
+++ b/signal.c
@@ -257,6 +257,7 @@ static VALUE
 sig_signame(VALUE recv, VALUE signo)
 {
     const char *signame = signo2signm(NUM2INT(signo));
+    if (!signame) return Qnil;
     return rb_str_new_cstr(signame);
 }
 
diff --git a/test/ruby/test_signal.rb b/test/ruby/test_signal.rb
index 4a59aa66c8..781045d30a 100644
--- a/test/ruby/test_signal.rb
+++ b/test/ruby/test_signal.rb
@@ -218,6 +218,15 @@ class TestSignal < Test::Unit::TestCase
   end
 
   def test_signame
+    Signal.list.each do |name, num|
+      assert_equal(num, Signal.list[Signal.signame(num)], name)
+    end
+    assert_nil(Signal.signame(-1))
+    signums = Signal.list.invert
+    assert_nil(Signal.signame((1..1000).find {|num| !signums[num]}))
+  end
+
+  def test_signame_delivered
     10.times do
       IO.popen([EnvUtil.rubybin, "-e", <<EOS, :err => File::NULL]) do |child|
         Signal.trap("INT") do |signo|