A '(' character or an element type is required in the declaration of element type "viewer_rating" error

I keep getting this error within my DTD code. I have tried adding ")" and other characters but nothing seems to work.

<?xml version="1.0" encoding="UTF-8"?>

<!-- New document created with EditiX at Sun Jul 13 10:48:54 AST 2014 -->

<!DOCTYPE movies
[
<!ELEMENT movies-movie (movies-movie*)>  
<!ELEMENT movie (title, genre, movie_rating, viewer_rating, summary, year, director+, runtime, studio, actors+)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT genre (action|comedy|drama|family|foreign|horror|musical|other)>
<!ELEMENT movie_rating (G|PG|PG-13|R|NC-17)>
<!ELEMENT viewer_rating ( | 1 | 2 | 3 | 4 | 5)><!--receive error here -->

<!ELEMENT summary (#PCDATA)>
<!ELEMENT year (#PCDATA)>
<!ELEMENT director (#PCDATA)>
<!ELEMENT runtime (#PCDATA)>
<!ELEMENT studio (#PCDATA)>
<!ELEMENT actors (#PCDATA)>
<!ATTLIST actors id CDATA #REQUIRED>
]>

Any help would be appreciated Thank you