diff --git a/OffsetCurve3d.cpp b/OffsetCurve3d.cpp
index 678ac65..54f78da 100644
--- a/OffsetCurve3d.cpp
+++ b/OffsetCurve3d.cpp
@@ -156,10 +156,14 @@ OffsetCurve3d::Make( const PNT5AXVECTOR& vPnt5Ax, double dOffDist, int nType)
    Vector3d vtDirPrevOff  = V_INVALID ;
    for ( int i = 1 ; i <= pCrv->GetCurveCount() ; ++i) {
       pCrvCurr = pCrv->GetNextCurve() ;
-      if ( pCrvCurr == nullptr  && bClosed  &&  vFlag[i] == OffsetCurve3d::AngType::ANG_CVEX)
+      if ( pCrvCurr == nullptr  &&  bClosed)
          pCrvCurr = pCrv->GetFirstCurve() ;
       Vector3d vtOffDir = vOffDir[i] ;
-      Vector3d vtDirCurr ; pCrvCurr->GetStartDir( vtDirCurr) ;
+      Vector3d vtDirCurr ; 
+      if ( pCrvCurr != nullptr)
+         pCrvCurr->GetStartDir( vtDirCurr) ;
+      else
+         vtDirCurr = vtDirPrev ;
       pCrvPrev->GetStartDir( vtDirPrev) ;
       Vector3d vtTang ;
       if ( vFlag[i] != OffsetCurve3d::AngType::ANG_CVEX)
@@ -176,7 +180,11 @@ OffsetCurve3d::Make( const PNT5AXVECTOR& vPnt5Ax, double dOffDist, int nType)
          dCorrK = 1 / sin( 90 - dHalfAlfa) ;
       }
 
-      Point3d ptP ; pCrvCurr->GetStartPoint( ptP) ;
+      Point3d ptP ;
+      if ( pCrvCurr != nullptr)
+         pCrvCurr->GetStartPoint( ptP) ;
+      else
+         pCrvPrev->GetEndPoint( ptP) ;
       dRadCorr = dOffDist ;
       ptP = ptP + dRadCorr * dCorrK * vtCorr ;
       // se secondo punto di angolo esterno di fianco, inserisco movimenti intermedi