diff --git a/app/main/views/send.py b/app/main/views/send.py
index 5df777946..83c1b3297 100644
--- a/app/main/views/send.py
+++ b/app/main/views/send.py
@@ -1,10 +1,10 @@
 import itertools
 from string import ascii_uppercase
-from io import BytesIO
 
 from contextlib import suppress
 from zipfile import BadZipFile
 from xlrd.biffh import XLRDError
+from werkzeug.routing import RequestRedirect
 
 from flask import (
     request,
@@ -25,7 +25,7 @@ from notifications_utils.columns import Columns
 from notifications_utils.recipients import RecipientCSV, first_column_headings, validate_and_format_phone_number
 
 from app.main import main
-from app.main.forms import CsvUploadForm, ChooseTimeForm, get_next_days_until, get_furthest_possible_scheduled_time
+from app.main.forms import CsvUploadForm, ChooseTimeForm, get_furthest_possible_scheduled_time
 from app.main.uploader import (
     s3upload,
     s3download
@@ -235,7 +235,13 @@ def send_from_api(service_id, template_id):
 def _check_messages(service_id, template_type, upload_id, letters_as_pdf=False):
 
     if not session.get('upload_data'):
-        return redirect(url_for('main.choose_template', service_id=service_id, template_type=template_type))
+        # if we just return a `redirect` (302) object here, we'll get errors when we try and unpack in the
+        # check_messages route - so raise a werkzeug.routing redirect to ensure that doesn't happen.
+
+        # NOTE: this is a 301 MOVED PERMANENTLY (httpstatus.es/301), so the browser will cache this redirect, and it'll
+        # *always* happen for that browser. _check_messages is only used by endpoints that contain `upload_id`, which
+        # is a one-time-use id (that ties to a given file in S3 that is already deleted if it's not in the session)
+        raise RequestRedirect(url_for('main.choose_template', service_id=service_id, template_type=template_type))
 
     users = user_api_client.get_users_for_service(service_id=service_id)
 
diff --git a/tests/app/main/views/test_send.py b/tests/app/main/views/test_send.py
index 73c7ddefa..452a04ae3 100644
--- a/tests/app/main/views/test_send.py
+++ b/tests/app/main/views/test_send.py
@@ -1,15 +1,16 @@
+import uuid
 from io import BytesIO
 from os import path
 from glob import glob
 import re
 from itertools import repeat
 from functools import partial
-from unittest.mock import Mock, patch
+from unittest.mock import patch
+from urllib.parse import urlparse
 
 import pytest
 from bs4 import BeautifulSoup
 from flask import url_for
-from notifications_utils.template import LetterPreviewTemplate
 
 from tests import validate_route_permission
 
@@ -882,3 +883,23 @@ def test_check_messages_shows_over_max_row_error(
         'Notify can process up to 11,111 rows at once. '
         'Your file has 99,999 rows.'
     )
+
+
+def test_check_messages_goes_to_select_template_if_no_upload_data(logged_in_client):
+    service_id = uuid.uuid4()
+
+    response = logged_in_client.get(url_for(
+        'main.check_messages',
+        service_id=service_id,
+        template_type='sms',
+        upload_id=uuid.uuid4(),
+    ))
+
+    # permanent redirect
+    assert response.status_code == 301
+    assert response.location == url_for(
+        'main.choose_template',
+        service_id=service_id,
+        template_type='sms',
+        _external=True
+    )