--- a/hglib.lua	Fri Sep 16 07:55:11 2016 +0800
+++ b/hglib.lua	Fri Sep 16 10:40:32 2016 +0800
@@ -149,6 +149,7 @@
 		elseif channel == 'd' then
 			d = d .. message
 		elseif channel:lower() ~= channel then
+			e = e .. '\nhglib: unexpected data on required channel "' .. channel .. '"'
 			return nil, o, e, d
 		end
 	end