OK, now I understand, maybe ... ,

I tried this but didn't made it work. I used:

With rngForm.Borders(xlEdgeTop)
If .LineStyle < xlContinuous Then
.LineStyle = xlContinuous
End If
If .Weight < xlMedium Then
.Weight = xlMedium
End If
If .Color < RGB(255, 0, 0) Then
.Color = RGB(255, 0, 0)
End If
End With

.... but if rng had several border ranges, it passed by. But you use
IsNull(). That might make a different.

Kind regards
Tskogstrom