diff --git a/lua_controller/server.lua b/lua_controller/server.lua
index 62cea21..e59fcb8 100644
--- a/lua_controller/server.lua
+++ b/lua_controller/server.lua
@@ -122,6 +122,8 @@ minetest.register_craft({
 local function calc_size(v)
 	if type(v) == "number" then
 		return 1
+	elseif type(v) == "boolean" then
+		return 1
 	elseif v == nil then
 		return 0
 	elseif type(v) == "string" then