"Compile Error: Expected: =" when trying to call a sub

[mikeycorn]

I'm trying to call a sub with three parameters.

CenterPrint(Titl, "Arial", 24)

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Private Sub CenterPrint(ByVal Text As String, Optional ByVal FName As String, Optional ByVal FSize As Integer)
  If FName Then Printer.Font.Name = FName
  If FSize Then Printer.Font.Size = FSize
  Printer.CurrentX = Printer.ScaleX / 2 - Printer.TextWidth(Text) / 2
  Printer.Print Text
End Sub

Why does VB tell me "Compile Error: Expected: ="