Problem with fetching large amount of text into form item

I've got the following problem: I'm keeping large text files in a table, where each record hold a row of the file. I'm using the code below for fetching specific file text into a form item. Though the item defined as long, and there should be no limitation on the amount of data it could hold, when the file is too big (> 32K), I've got an VALUE_ERROR exception (on the line marked with ****), and can't extract all the data into the field.
Does anybody have an idea how can I solve this problem? Will UserExit can be useful on such a case?

thanks in advanced,
Maoz

DECLARE
  line_val VARCHAR2(2000);
  CURSOR get_text IS
   SELECT long_text FROM long_text_table    WHERE file_key=:file_key
   ORDER BY row_num;

 BEGIN
   OPEN get_text;
   LOOP

      FETCH get_text INTO line_val;
        IF get_text%NOTFOUND THEN
            EXIT;
        END IF;
     :long_text_value := :long_text_value||line_val; -- ****
     next_record;