diff --git a/src/BRepTools/BRepTools_NurbsConvertModification.cxx b/src/BRepTools/BRepTools_NurbsConvertModification.cxx
index 57e4d9806d..d2f47f8496 100644
--- a/src/BRepTools/BRepTools_NurbsConvertModification.cxx
+++ b/src/BRepTools/BRepTools_NurbsConvertModification.cxx
@@ -508,24 +508,25 @@ Standard_Boolean BRepTools_NurbsConvertModification::NewPolygon(const TopoDS_Edg
     return Standard_False;
   }
 
-  // update parameters of polygon
-  if (thePoly->HasParameters())
+  if (!thePoly->HasParameters())
   {
-    Standard_Real      aTol = BRep_Tool::Tolerance(theEdge);
-    Standard_Real      aFirst, aLast;
-    Handle(Geom_Curve) aCurve    = BRep_Tool::Curve(theEdge, aFirst, aLast);
-    Handle(Geom_Curve) aNewCurve = newCurve(myMap, theEdge, aFirst, aLast);
-    if (aCurve.IsNull() || aNewCurve.IsNull()) // skip processing degenerated edges
-    {
-      return Standard_False;
-    }
-    TColStd_Array1OfReal& aParams = thePoly->ChangeParameters();
-    for (Standard_Integer anInd = aParams.Lower(); anInd <= aParams.Upper(); ++anInd)
-    {
-      Standard_Real& aParam = aParams(anInd);
-      gp_Pnt         aPoint = aCurve->Value(aParam);
-      newParameter(aPoint, aNewCurve, aFirst, aLast, aTol, aParam);
-    }
+    return Standard_False;
+  }
+  // update parameters of polygon
+  Standard_Real      aTol = BRep_Tool::Tolerance(theEdge);
+  Standard_Real      aFirst, aLast;
+  Handle(Geom_Curve) aCurve    = BRep_Tool::Curve(theEdge, aFirst, aLast);
+  Handle(Geom_Curve) aNewCurve = newCurve(myMap, theEdge, aFirst, aLast);
+  if (aCurve.IsNull() || aNewCurve.IsNull()) // skip processing degenerated edges
+  {
+    return Standard_False;
+  }
+  TColStd_Array1OfReal& aParams = thePoly->ChangeParameters();
+  for (Standard_Integer anInd = aParams.Lower(); anInd <= aParams.Upper(); ++anInd)
+  {
+    Standard_Real& aParam = aParams(anInd);
+    gp_Pnt         aPoint = aCurve->Value(aParam);
+    newParameter(aPoint, aNewCurve, aFirst, aLast, aTol, aParam);
   }
   return Standard_True;
 }