diff --git a/EGkTriangle3d.h b/EGkTriangle3d.h
index 1c8dbfb..9e5e1c8 100644
--- a/EGkTriangle3d.h
+++ b/EGkTriangle3d.h
@@ -34,15 +34,15 @@ class Triangle3d
                 ptP[nId] = ptV ;
                 return true ;
               }
-      bool Validate( void)
+      bool Validate( bool bOverwrite = false)
               { if ( AreSamePointApprox( ptP[0], ptP[1])  ||  AreSamePointApprox( ptP[0], ptP[2]))
                    return false ;
                 Vector3d vtV = ( ptP[1] - ptP[0]) ^ ( ptP[2] - ptP[0]) ;
                 vtV.Normalize() ;
-                if ( ! vtN.IsZero())
-                   return AreSameVectorApprox( vtV, vtN) ;
-                vtN = vtV ;
-                return true ;
+                bool bOk = ( vtN.IsZero() || AreSameVectorApprox( vtV, vtN)) ;
+                if ( bOverwrite)
+                   vtN = vtV ;
+                return bOk ;
               }
       bool ToGlob( const Frame3d& frRef)
               { return ( ptP[0].ToGlob( frRef)  &&  ptP[1].ToGlob( frRef)  &&  ptP[2].ToGlob( frRef)) ; }