diff --git a/app/celery/letters_pdf_tasks.py b/app/celery/letters_pdf_tasks.py
index a2431fbd1..5f715c97d 100644
--- a/app/celery/letters_pdf_tasks.py
+++ b/app/celery/letters_pdf_tasks.py
@@ -178,7 +178,6 @@ def collate_letter_pdfs_to_be_sent():
 
 def get_key_and_size_of_letters_to_be_sent_to_print(print_run_deadline, postage):
     letters_awaiting_sending = dao_get_letters_to_be_printed(print_run_deadline, postage)
-    letter_pdfs = []
     for letter in letters_awaiting_sending:
         try:
             letter_file_name = get_letter_pdf_filename(
@@ -188,17 +187,15 @@ def get_key_and_size_of_letters_to_be_sent_to_print(print_run_deadline, postage)
                 postage=letter.postage
             )
             letter_head = s3.head_s3_object(current_app.config['LETTERS_PDF_BUCKET_NAME'], letter_file_name)
-            letter_pdfs.append({
+            yield {
                 "Key": letter_file_name,
                 "Size": letter_head['ContentLength'],
                 "ServiceId": str(letter.service.id)
-            })
+            }
         except BotoClientError as e:
             current_app.logger.exception(
                 f"Error getting letter from bucket for notification: {letter.id} with reference: {letter.reference}", e)
 
-    return letter_pdfs
-
 
 def group_letters(letter_pdfs):
     """
diff --git a/app/dao/notifications_dao.py b/app/dao/notifications_dao.py
index b8570a451..cf9f143d4 100644
--- a/app/dao/notifications_dao.py
+++ b/app/dao/notifications_dao.py
@@ -730,7 +730,7 @@ def dao_get_letters_to_be_printed(print_run_deadline, postage):
     ).order_by(
         Notification.service_id,
         Notification.created_at
-    ).all()
+    )
     return notifications
 
 
diff --git a/tests/app/celery/test_letters_pdf_tasks.py b/tests/app/celery/test_letters_pdf_tasks.py
index 6e1664fef..6badc3bce 100644
--- a/tests/app/celery/test_letters_pdf_tasks.py
+++ b/tests/app/celery/test_letters_pdf_tasks.py
@@ -223,7 +223,9 @@ def test_get_key_and_size_of_letters_to_be_sent_to_print(notify_api, mocker, sam
         {'ContentLength': 3},
     ])
 
-    results = get_key_and_size_of_letters_to_be_sent_to_print(datetime.now() - timedelta(minutes=30), postage='second')
+    results = list(
+        get_key_and_size_of_letters_to_be_sent_to_print(datetime.now() - timedelta(minutes=30), postage='second')
+    )
 
     assert mock_s3.call_count == 3
     mock_s3.assert_has_calls(
@@ -284,7 +286,9 @@ def test_get_key_and_size_of_letters_to_be_sent_to_print_catches_exception(
         ClientError(error_response, "File not found")
     ])
 
-    results = get_key_and_size_of_letters_to_be_sent_to_print(datetime.now() - timedelta(minutes=30), postage='second')
+    results = list(
+        get_key_and_size_of_letters_to_be_sent_to_print(datetime.now() - timedelta(minutes=30), postage='second')
+    )
 
     assert mock_head_s3_object.call_count == 2
     mock_head_s3_object.assert_has_calls(
diff --git a/tests/app/dao/notification_dao/test_notification_dao.py b/tests/app/dao/notification_dao/test_notification_dao.py
index 375bfafd6..8b8717740 100644
--- a/tests/app/dao/notification_dao/test_notification_dao.py
+++ b/tests/app/dao/notification_dao/test_notification_dao.py
@@ -1692,6 +1692,6 @@ def test_letters_to_be_printed_sort_by_service(notify_db_session):
     notification_2 = create_notification(template=first_template, created_at=datetime(2020, 12, 1, 12, 30))
     notification_3 = create_notification(template=second_template, created_at=datetime(2020, 12, 1, 8, 30))
 
-    results = dao_get_letters_to_be_printed(print_run_deadline=datetime(2020, 12, 1, 17, 30), postage='second')
+    results = list(dao_get_letters_to_be_printed(print_run_deadline=datetime(2020, 12, 1, 17, 30), postage='second'))
     assert len(results) == 3
     assert results == [notification_1, notification_2, notification_3]