diff --git a/inferium-harvester.lua b/inferium-harvester.lua
index df39604..da61c62 100644
--- a/inferium-harvester.lua
+++ b/inferium-harvester.lua
@@ -385,8 +385,8 @@ local function replantProcedure()
     error('cannot fetch the remote plan')
   end
 
-  local seedsToRemove = utils.difference(localPlan, remotePlan)
-  local seedsToPlant = utils.difference(remotePlan, localPlan)
+  local seedsToRemove = utils.shallowDiff(localPlan, remotePlan)
+  local seedsToPlant = utils.shallowDiff(remotePlan, localPlan)
 
   if utils.sizeof(seedsToRemove) > 0 then
     print('nb seeds to remove: ' .. utils.sizeof(seedsToRemove))
diff --git a/libs/utils.lua b/libs/utils.lua
index 424481a..423981a 100644
--- a/libs/utils.lua
+++ b/libs/utils.lua
@@ -12,15 +12,31 @@ utils.sizeof = function(t)
   return size
 end
 
-utils.difference = function(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
+utils.shallowDiff = function(a, b)
+  local counters = {}
+
+  for k,v in pairs(a) do
+    local currentCounter = counters[v] or 0
+    counters[v] = currentCounter + 1
+  end
+
+  for k,v in pairs(b) do
+    if counters[v] then
+      counters[v] = counters[v] - 1
+    end
+  end
+
   local ret = {}
   local n = 0
+
   for k,v in pairs(a) do
-      if aa[v] then n=n+1 ret[n]=v end
+    if counters[v] and counters[v] > 0 then
+      counters[v] = counters[v] - 1
+      n = n + 1
+      ret[n] = v
+    end
   end
+
   return ret
 end