diff --git a/lib/net/http/response.rb b/lib/net/http/response.rb
index e2964c41a1..1351d7b2d2 100644
--- a/lib/net/http/response.rb
+++ b/lib/net/http/response.rb
@@ -117,7 +117,9 @@ class Net::HTTPResponse
   end
 
   def error!   #:nodoc:
-    raise error_type().new(@code + ' ' + @message.dump, self)
+    message = @code
+    message += ' ' + @message.dump if @message
+    raise error_type().new(message, self)
   end
 
   def error_type   #:nodoc:
diff --git a/test/net/http/test_httpresponse.rb b/test/net/http/test_httpresponse.rb
index a494b7fb85..a67add7c88 100644
--- a/test/net/http/test_httpresponse.rb
+++ b/test/net/http/test_httpresponse.rb
@@ -385,6 +385,22 @@ EOS
     assert_equal(nil, res.message)
   end
 
+  def test_raises_exception_with_missing_reason
+    io = dummy_io(<<EOS)
+HTTP/1.1 404
+Content-Length: 5
+Connection: close
+
+hello
+EOS
+
+    res = Net::HTTPResponse.read_new(io)
+    assert_equal(nil, res.message)
+    assert_raise Net::HTTPServerException do
+      res.error!
+    end
+  end
+
 private
 
   def dummy_io(str)