Zip Code Placeholder

[rdw1260]

I'm using Access 2003. I have the following input mask: 00000\-9999;;_. When
the zip code data has 5 characters rather than 9, it displays the placeholder
"-". I used the following expression:
(IIf(Len([HomePostalCode])>=9,Left([HomePostalCode],5) & "-" &
Right([HomePostalCode],4),Left([HomePostalCode],5)))) in the query for the
form. It worked, but now I cannot enter any zip code data.

I'm a novice. How do I get the zip code field to not display the placeholder
when the zip code field has, 5 characters.

Thanks for any responses.