diff --git a/app/celery/letters_pdf_tasks.py b/app/celery/letters_pdf_tasks.py
index 3ee3822a0..6a0a72e7f 100644
--- a/app/celery/letters_pdf_tasks.py
+++ b/app/celery/letters_pdf_tasks.py
@@ -15,7 +15,7 @@ from celery.exceptions import MaxRetriesExceededError
 from notifications_utils.statsd_decorators import statsd
 from notifications_utils.s3 import s3upload
 
-from app import notify_celery
+from app import encryption, notify_celery
 from app.aws import s3
 from app.config import QueueNames, TaskNames
 from app.dao.notifications_dao import (
@@ -302,14 +302,12 @@ def sanitise_letter(self, filename):
 
 
 @notify_celery.task(name='process-sanitised-letter')
-def process_sanitised_letter(
-    page_count,
-    message,
-    invalid_pages,
-    validation_status,
-    filename,
-    notification_id,
-):
+def process_sanitised_letter(sanitise_data):
+    letter_details = encryption.decrypt(sanitise_data)
+
+    filename = letter_details['filename']
+    notification_id = letter_details['notification_id']
+
     current_app.logger.info('Processing sanitised letter with id {}'.format(notification_id))
     notification = get_notification_by_id(notification_id, _raise=True)
 
@@ -323,7 +321,7 @@ def process_sanitised_letter(
     try:
         original_pdf_object = s3.get_s3_object(current_app.config['LETTERS_SCAN_BUCKET_NAME'], filename)
 
-        if validation_status == 'failed':
+        if letter_details['validation_status'] == 'failed':
             current_app.logger.info('Processing invalid precompiled pdf with id {} (file {})'.format(
                 notification_id, filename))
 
@@ -331,16 +329,16 @@ def process_sanitised_letter(
                 notification=notification,
                 filename=filename,
                 scan_pdf_object=original_pdf_object,
-                message=message,
-                invalid_pages=invalid_pages,
-                page_count=page_count,
+                message=letter_details['message'],
+                invalid_pages=letter_details['invalid_pages'],
+                page_count=letter_details['page_count'],
             )
             return
 
         current_app.logger.info('Processing valid precompiled pdf with id {} (file {})'.format(
             notification_id, filename))
 
-        billable_units = get_billable_units_for_letter_page_count(page_count)
+        billable_units = get_billable_units_for_letter_page_count(letter_details['page_count'])
         is_test_key = notification.key_type == KEY_TYPE_TEST
 
         move_sanitised_letter_to_test_or_live_pdf_bucket(filename, is_test_key, notification.created_at)
diff --git a/tests/app/celery/test_letters_pdf_tasks.py b/tests/app/celery/test_letters_pdf_tasks.py
index 4e6ade009..bc280dce7 100644
--- a/tests/app/celery/test_letters_pdf_tasks.py
+++ b/tests/app/celery/test_letters_pdf_tasks.py
@@ -13,6 +13,7 @@ from celery.exceptions import MaxRetriesExceededError, Retry
 from requests import RequestException
 from sqlalchemy.orm.exc import NoResultFound
 
+from app import encryption
 from app.errors import VirusScanError
 from app.exceptions import NotificationTechnicalFailureException
 from app.celery.letters_pdf_tasks import (
@@ -773,14 +774,15 @@ def test_process_sanitised_letter_with_valid_letter(
     sample_letter_notification.billable_units = 1
     sample_letter_notification.created_at = datetime(2018, 7, 1, 12)
 
-    process_sanitised_letter(
-        page_count=2,
-        message=None,
-        invalid_pages=None,
-        validation_status='passed',
-        filename=filename,
-        notification_id=str(sample_letter_notification.id)
-    )
+    encrypted_data = encryption.encrypt({
+        'page_count': 2,
+        'message': None,
+        'invalid_pages': None,
+        'validation_status': 'passed',
+        'filename': filename,
+        'notification_id': str(sample_letter_notification.id)
+    })
+    process_sanitised_letter(encrypted_data)
 
     assert sample_letter_notification.status == expected_status
     assert sample_letter_notification.billable_units == 1
@@ -815,14 +817,15 @@ def test_process_sanitised_letter_with_invalid_letter(sample_letter_notification
     sample_letter_notification.billable_units = 1
     sample_letter_notification.created_at = datetime(2018, 7, 1, 12)
 
-    process_sanitised_letter(
-        page_count=2,
-        message='content-outside-printable-area',
-        invalid_pages=[1],
-        validation_status='failed',
-        filename=filename,
-        notification_id=str(sample_letter_notification.id)
-    )
+    encrypted_data = encryption.encrypt({
+        'page_count': 2,
+        'message': 'content-outside-printable-area',
+        'invalid_pages': [1],
+        'validation_status': 'failed',
+        'filename': filename,
+        'notification_id': str(sample_letter_notification.id)
+    })
+    process_sanitised_letter(encrypted_data)
 
     assert sample_letter_notification.status == NOTIFICATION_VALIDATION_FAILED
     assert sample_letter_notification.billable_units == 0
@@ -842,14 +845,15 @@ def test_process_sanitised_letter_when_letter_status_is_not_pending_virus_scan(
     mock_s3 = mocker.patch('app.celery.letters_pdf_tasks.s3')
     sample_letter_notification.status = NOTIFICATION_CREATED
 
-    process_sanitised_letter(
-        page_count=2,
-        message=None,
-        invalid_pages=None,
-        validation_status='passed',
-        filename='NOTIFY.{}'.format(sample_letter_notification.reference),
-        notification_id=str(sample_letter_notification.id)
-    )
+    encrypted_data = encryption.encrypt({
+        'page_count': 2,
+        'message': None,
+        'invalid_pages': None,
+        'validation_status': 'passed',
+        'filename': 'NOTIFY.{}'.format(sample_letter_notification.reference),
+        'notification_id': str(sample_letter_notification.id)
+    })
+    process_sanitised_letter(encrypted_data)
 
     assert not mock_s3.called
 
@@ -861,15 +865,17 @@ def test_process_sanitised_letter_puts_letter_into_tech_failure_for_boto_errors(
     mocker.patch('app.celery.letters_pdf_tasks.s3.get_s3_object', side_effect=ClientError({}, 'operation_name'))
     sample_letter_notification.status = NOTIFICATION_PENDING_VIRUS_CHECK
 
+    encrypted_data = encryption.encrypt({
+        'page_count': 2,
+        'message': None,
+        'invalid_pages': None,
+        'validation_status': 'passed',
+        'filename': 'NOTIFY.{}'.format(sample_letter_notification.reference),
+        'notification_id': str(sample_letter_notification.id)
+    })
+
     with pytest.raises(NotificationTechnicalFailureException):
-        process_sanitised_letter(
-            page_count=2,
-            message=None,
-            invalid_pages=None,
-            validation_status='passed',
-            filename='NOTIFY.{}'.format(sample_letter_notification.reference),
-            notification_id=str(sample_letter_notification.id)
-        )
+        process_sanitised_letter(encrypted_data)
 
     assert sample_letter_notification.status == NOTIFICATION_TECHNICAL_FAILURE