diff --git a/LuaLibs/WallExec.lua b/LuaLibs/WallExec.lua
index 6c7866b..6217c26 100644
--- a/LuaLibs/WallExec.lua
+++ b/LuaLibs/WallExec.lua
@@ -1329,7 +1329,7 @@ function WallExec.ProcessFeatures()
       if Proc.Double and Proc.Double > 0 then
          for j = 1, #vProc do
             local ProcMirror = vProc[j]
-            if Proc.Mirror.Id == ProcMirror.Id then
+            if Proc.Mirror and ( Proc.Mirror.Id == ProcMirror.Id) then
                -- per i fori l'operazione si basa sulla geometria ausiliaria
                if Proc.TopologyLongName == 'DRILLING' then
                   local AuxId = EgtGetInfo( ProcMirror.Id, 'AUXID', 'i') or 0