diff --git a/LuaLibs/ProcessMortise.lua b/LuaLibs/ProcessMortise.lua
index 24419d2..e757b5a 100644
--- a/LuaLibs/ProcessMortise.lua
+++ b/LuaLibs/ProcessMortise.lua
@@ -256,7 +256,7 @@ function ProcessMortise.VerifyMortiseOrPocket( Proc, dDiam, dDepth, dMaxTotLen,
       sPocketing = ML.FindPocketing( sType, dDiam, 0, dMaxTotLen, bExcludeH2)
    end
    if not sPocketing then
-      return false
+      return nil
    end
    -- recupero i dati dell'utensile
    local dMaxDepth = 0