Proper Case not working

Hi,

I am trying to force the input of a text box to be changed to Proper Case (First letter of each word capitalised) but for some reason it is not working. I am using the fucntion below, can anybody see what I am doing wrong?

Private Sub txtFirstname_LostFocus()

    Me.txtFirstname = StrConv(Me.txtFirstname, vbProperCase)

End Sub

Thanks,
David