diff --git a/builtin/game/register.lua b/builtin/game/register.lua
index 3edab04..d111e5c 100644
--- a/builtin/game/register.lua
+++ b/builtin/game/register.lua
@@ -514,11 +514,17 @@ local function make_registration_wrap(reg_fn_name, clear_fn_name)
 end
 
 local function make_wrap_deregistration(reg_fn, clear_fn, list)
-	local unregister = function (unregistered_key)
+	local unregister = function (key)
+		if type(key) ~= "string" then
+			error("key is not a string", 2)
+		end
+		if not list[key] then
+			error("Attempt to unregister non-existent element - '" .. key .. "'", 2)
+		end
 		local temporary_list = table.copy(list)
 		clear_fn()
 		for k,v in pairs(temporary_list) do
-			if unregistered_key ~= k then
+			if key ~= k then
 				reg_fn(v)
 			end
 		end
@@ -564,7 +570,8 @@ core.registered_biomes      = make_registration_wrap("register_biome",      "cle
 core.registered_ores        = make_registration_wrap("register_ore",        "clear_registered_ores")
 core.registered_decorations = make_registration_wrap("register_decoration", "clear_registered_decorations")
 
-core.unregister_biome = make_wrap_deregistration(core.register_biome, core.clear_registered_biomes, core.registered_biomes)
+core.unregister_biome = make_wrap_deregistration(core.register_biome,
+		core.clear_registered_biomes, core.registered_biomes)
 
 core.registered_on_chat_messages, core.register_on_chat_message = make_registration()
 core.registered_globalsteps, core.register_globalstep = make_registration()