Incomplete SQL error in SQLite database

I've a SQLite script which initializes a DB (SQLite 3.8.2), created as follows:

sqlite3 -init database_creation.sql sample.db

The script file is like:

 // Some `CREATE TABLE` statements

 CREATE TRIGGER update_totalprice AFTER UPDATE
   OF price, amount, boxes ON product
   BEGIN UPDATE product SET totalprice = price * boxes * amount
   WHERE idproduct = NEW.idproduct; END

 // Some `INSERT` statements.

But it generates the following error:

Error: incomplete SQL: CREATE TRIGGER update_totalprice AFTER UPDATE
   OF price, amount, boxes ON product
   BEGIN UPDATE product SET totalprice = price * boxes * amount
   WHERE idproduct = NEW.idproduct; END

// The rest of the file to the end.

I'm sure there're syntax errors nor creating the tables neither inserting the test rows, because if I comment the CREATE TRIGGER statement all works perfectly fine, and I don't find the syntax error either.