diff --git a/doors_chest.lua b/doors_chest.lua
index 2793b82..fa234a2 100644
--- a/doors_chest.lua
+++ b/doors_chest.lua
@@ -740,6 +740,11 @@ minetest.register_on_player_receive_fields(function(player, formname, fields)
 
 	elseif fields.protect_name or fields.protect_rename then
 
+		if fields.protect_name ~= string.match(fields.protect_name, "[%w%s_-]+")
+		or fields.protect_name:len() > 35 then
+			return
+		end
+
 		-- change chest infotext to display name
 		if fields.protect_name ~= "" then