diff --git a/inferium-harvester.lua b/inferium-harvester.lua
index c411e7d..dc9f330 100644
--- a/inferium-harvester.lua
+++ b/inferium-harvester.lua
@@ -39,16 +39,16 @@ local function sizeof(t)
   return size
 end
 
-local function difference(a, b)
-  local ai = {}
-  local r = {}
-
-  for k,v in pairs(a) do r[k] = v; ai[v]=true end
-  for k,v in pairs(b) do
-      if ai[v]~=nil then   r[k] = nil   end
+function difference(a, b)
+  local aa = {}
+  for k,v in pairs(a) do aa[v]=true end
+  for k,v in pairs(b) do aa[v]=nil end
+  local ret = {}
+  local n = 0
+  for k,v in pairs(a) do
+      if aa[v] then n=n+1 ret[n]=v end
   end
-
-  return r
+  return ret
 end
 
 local function shallowClone(t)