diff --git a/storage.lua b/storage.lua
index b2a33d1..40990bb 100644
--- a/storage.lua
+++ b/storage.lua
@@ -57,7 +57,7 @@ function mail.sort_messages(unsorted_messages, sortfield, sortdirection)
 		table.insert(messages, unsorted_messages[1])
 		table.remove(unsorted_messages, 1)
 		-- sort messages
-		for i, unsorted_msg in ipairs(unsorted_messages) do
+		for _, unsorted_msg in ipairs(unsorted_messages) do
 			local is_message_sorted = false
 			for j, sorted_msg in ipairs(messages) do
 				if sortfield == "1" and unsorted_msg.from >= sorted_msg.from then -- for inbox
diff --git a/ui/events.lua b/ui/events.lua
index 9637a0a..8722ad4 100644
--- a/ui/events.lua
+++ b/ui/events.lua
@@ -7,7 +7,7 @@ minetest.register_on_player_receive_fields(function(player, formname, fields)
 
     -- split inbox and sent msgs for different tests
     local entry = mail.get_storage_entry(name)
-    
+
     local messagesInboxUnAnalyzed = entry.inbox
     local messagesOutBoxUnAnalyzed = entry.outbox
     local messagesDrafts = entry.drafts
@@ -24,17 +24,17 @@ minetest.register_on_player_receive_fields(function(player, formname, fields)
 
     -- then sort them
 
-    local sortfield = fields.sortfield
-    local sortdirection = fields.sortdirection
+    local sortfield = tostring(fields.sortfield)
+    local sortdirection = tostring(fields.sortdirection)
     if not sortfield or sortfield == "" or sortfield == "0" then
-        sortfield = 3
+        sortfield = "3"
     end
     if not sortdirection or sortdirection == "" or sortdirection == "0" then
-        sortdirection = 1
+        sortdirection = "1"
     end
 
-    local messagesInbox = mail.sort_messages(messagesInboxFiltered, tostring(sortfield), tostring(sortdirection), filter)
-    local messagesSent = mail.sort_messages(messagesOutboxFiltered, tostring(sortfield), tostring(sortdirection), filter)
+    local messagesInbox = mail.sort_messages(messagesInboxFiltered, sortfield, sortdirection, filter)
+    local messagesSent = mail.sort_messages(messagesOutboxFiltered, sortfield, sortdirection, filter)
 
     if fields.inbox then -- inbox table
         local evt = minetest.explode_table_event(fields.inbox)
diff --git a/ui/outbox.lua b/ui/outbox.lua
index 23df9be..3466e5e 100644
--- a/ui/outbox.lua
+++ b/ui/outbox.lua
@@ -42,7 +42,7 @@ function mail.show_sent(name, sortfield, sortdirection, filter)
 		table[0,0.7;5.75,8.35;sent;#999,]] .. S("To") .. "," .. S("Subject")
 	local formspec = { sent_formspec }
 	local entry = mail.get_storage_entry(name)
-    local messages = mail.sort_messages(mail.filter_messages(entry.outbox, filter), tostring(sortfield), tostring(sortdirection))
+    local messages = mail.sort_messages(mail.filter_messages(entry.outbox, filter), sortfield, sortdirection)
 
 	mail.message_drafts[name] = nil