diff --git a/concord/system.lua b/concord/system.lua
index 3db2a44..1b2be75 100644
--- a/concord/system.lua
+++ b/concord/system.lua
@@ -47,6 +47,7 @@ System.mt = {
 }
 
 local validateFilters = function (definition)
+   if not definition then return {} end
    local filters = {}
 
    for name, componentsList in pairs(definition) do