diff --git a/data/computercraft/lua/rom/modules/main/rc/thread.lua b/data/computercraft/lua/rom/modules/main/rc/thread.lua
index 1238ff5..d375f37 100644
--- a/data/computercraft/lua/rom/modules/main/rc/thread.lua
+++ b/data/computercraft/lua/rom/modules/main/rc/thread.lua
@@ -103,6 +103,9 @@ function api.exists(id)
 end
 
 function api.id()
+  if not current then
+    error("No current thread - are you calling this outside a thread?")
+  end
   return current.id
 end