diff --git a/stock-manager.lua b/stock-manager.lua
index 43ef4c8..e912b81 100644
--- a/stock-manager.lua
+++ b/stock-manager.lua
@@ -18,7 +18,7 @@ local SLEEP_T = 10
 function remove_waste(source, discard_rest)
     local amounts_to_keep = KEEP_ONLY
     local discard = function (item, amt, dest)
-        peripheral.call(source, "requestFiltered", dest,
+        peripheral.call(source, "requestFiltered", dest
             {
                 name = item.name,
                 _requestCount = amt,
@@ -29,7 +29,10 @@ function remove_waste(source, discard_rest)
         if amounts_to_keep[item.name] ~= nil then
             local excess = item.count - amounts_to_keep[item.name][1]
             if excess > 0 then
+                amounts_to_keep[item.name][1] = 0
                 discard(item, excess, amounts_to_keep[item.name][2])
+            else
+                amounts_to_keep[item.name][1] = -excess
             end
         elseif DISCARD_REST then
             discard(item, amt, DISCARD_ADDR)