diff --git a/lualib/sprotoparser.lua b/lualib/sprotoparser.lua
index f6b24399..4728368e 100644
--- a/lualib/sprotoparser.lua
+++ b/lualib/sprotoparser.lua
@@ -316,6 +316,7 @@ local function packgroup(t,p)
 		alltypes[name] = #alltypes
 		table.insert(alltypes, name)
 	end
+	table.sort(alltypes)	-- make result stable
 	tt = {}
 	for _,name in ipairs(alltypes) do
 		table.insert(tt, packtype(name, t[name], alltypes))