--- a/spec/util_stanza_spec.lua	Mon Nov 25 20:52:03 2019 +0100
+++ b/spec/util_stanza_spec.lua	Mon Nov 25 20:59:36 2019 +0100
@@ -191,13 +191,14 @@
 			local s = st.stanza("s", { to = "touser", from = "fromuser", id = "123" })
 				:tag("child1");
 			-- Make reply stanza
-			local r = st.error_reply(s, "cancel", "service-unavailable");
+			local r = st.error_reply(s, "cancel", "service-unavailable", nil, "host");
 			assert.are.equal(r.name, s.name);
 			assert.are.equal(r.id, s.id);
 			assert.are.equal(r.attr.to, s.attr.from);
 			assert.are.equal(r.attr.from, s.attr.to);
 			assert.are.equal(#r.tags, 1);
 			assert.are.equal(r.tags[1].tags[1].name, "service-unavailable");
+			assert.are.equal(r.tags[1].attr.by, "host");
 		end);
 
 		it("should work for <iq get>", function()

--- a/util/stanza.lua	Mon Nov 25 20:52:03 2019 +0100
+++ b/util/stanza.lua	Mon Nov 25 20:59:36 2019 +0100
@@ -447,7 +447,7 @@
 end
 
 local xmpp_stanzas_attr = { xmlns = xmlns_stanzas };
-local function error_reply(orig, error_type, condition, error_message)
+local function error_reply(orig, error_type, condition, error_message, error_by)
 	if not is_stanza(orig) then
 		error("bad argument to error_reply: expected stanza, got "..type(orig));
 	elseif orig.attr.type == "error" then
@@ -455,7 +455,10 @@
 	end
 	local t = reply(orig);
 	t.attr.type = "error";
-	t:tag("error", {type = error_type}) --COMPAT: Some day xmlns:stanzas goes here
+	if t.attr.from == error_by then
+		error_by = nil;
+	end
+	t:tag("error", {type = error_type, by = error_by}) --COMPAT: Some day xmlns:stanzas goes here
 	:tag(condition, xmpp_stanzas_attr):up();
 	if error_message then t:text_tag("text", error_message, xmpp_stanzas_attr); end
 	return t; -- stanza ready for adding app-specific errors