diff --git a/CalcPocketing.cpp b/CalcPocketing.cpp
index fc4d685..3db077d 100644
--- a/CalcPocketing.cpp
+++ b/CalcPocketing.cpp
@@ -3741,6 +3741,8 @@ CalcTrapezoidSpiral( ICurveComposite* pCrvPocket, const Frame3d& frTrap, double
             }
 
          }
+         else if ( bInvertByRef)
+            pMCrv->Invert() ;
       }
    }