--- a/plugins/mod_storage_memory.lua	Wed Feb 27 10:27:17 2019 +0100
+++ b/plugins/mod_storage_memory.lua	Sat Mar 02 22:26:01 2019 +0100
@@ -3,6 +3,7 @@
 local envload = require "util.envload".envload;
 local st = require "util.stanza";
 local is_stanza = st.is_stanza or function (s) return getmetatable(s) == st.stanza_mt end
+local new_id = require "util.id".medium;
 
 local auto_purge_enabled = module:get_option_boolean("storage_memory_temporary", false);
 local auto_purge_stores = module:get_option_set("storage_memory_temporary_stores", {});
@@ -56,7 +57,7 @@
 	end
 	local v = { key = key, when = when, with = with, value = value };
 	if not key then
-		key = tostring(a):match"%x+$"..tostring(v):match"%x+$";
+		key = new_id();
 		v.key = key;
 	end
 	if a[key] then