Sub Worksheet_Change(ByVal Target As Range)
On Error GoTo Fin: If Target.Count > 1 Then Exit Sub
If Not Intersect(Target, [B5]) Is Nothing Then
If [B4] = "" Then
Application.EnableEvents = False
MsgBox "Attention, pensez à remplir B4"
[B5] = "": [B4].Select
End If
End If
Fin:
Application.EnableEvents = True
End Sub