Validation Option button VBA

Function GetTaille() As String
    Dim ctl As Control
    For Each ctl In taille.Controls
        If TypeOf ctl Is MSForms.OptionButton Then
            If ctl Then
                GetTaille = ctl.Caption
                Exit For
            End If
        End If
    Next
End Function

Private Sub b_validation_Click()
    Dim sTaille As String: sTaille = GetTaille()
     '.....
    ActiveCell.Offset(0, 4).Value = Application.Proper(GetTaille())  
End Sub