diff --git a/biofuel-manager.lua b/biofuel-manager.lua
index 335118a..c1424d6 100644
--- a/biofuel-manager.lua
+++ b/biofuel-manager.lua
@@ -116,7 +116,7 @@ function run (requester, ticker)
     return run(requester, ticker)
 end
 
-if arg[1] == "run" then
+if arg ~= nil and arg[1] == "run" then
     local requester = peripheral.wrap(MAIN_REQUESTER)
     local ticker = peripheral.wrap(SUBNET_TICKER)
     run(requester, ticker)