diff --git a/app/main/views/notifications.py b/app/main/views/notifications.py
index af887b48b..158c02635 100644
--- a/app/main/views/notifications.py
+++ b/app/main/views/notifications.py
@@ -18,6 +18,7 @@ from flask import (
     url_for,
 )
 from notifications_python_client.errors import APIError, HTTPError
+from notifications_utils import LETTER_MAX_PAGE_COUNT
 from notifications_utils.letter_timings import (
     get_letter_timings,
     letter_can_be_cancelled,
@@ -79,6 +80,13 @@ def view_notification(service_id, notification_id):
             )
     else:
         page_count = get_page_count_for_letter(notification['template'], values=personalisation)
+        if page_count and page_count > LETTER_MAX_PAGE_COUNT:
+            # when a templated letter is sent via the api and the personalisation pushes
+            # the page count over 10 we need to validate that. The letter is not in validation failed,
+            # this will enable us to show the error. Perhaps there is a better way to do this.
+            error_message = get_letter_validation_error(
+                "letter-too-long", [1], page_count
+            )
 
     if notification.get('postage'):
         if notification["status"] == "validation-failed":
diff --git a/tests/app/main/views/test_notifications.py b/tests/app/main/views/test_notifications.py
index 069b34d78..d827f8878 100644
--- a/tests/app/main/views/test_notifications.py
+++ b/tests/app/main/views/test_notifications.py
@@ -677,6 +677,29 @@ def test_should_show_image_of_letter_notification_that_failed_validation(
     assert response.get_data(as_text=True) == 'foo', metadata
 
 
+def test_should_show_image_of_templated_letter_notification_that_failed_validation_because_letter_is_too_long(
+    client_request,
+    mocker,
+    fake_uuid,
+):
+    notification = create_notification(
+        notification_status='validation-failed',
+        template_type='letter')
+    mocker.patch('app.notification_api_client.get_notification', return_value=notification)
+    mocker.patch('app.main.views.notifications.get_page_count_for_letter', return_value=11)
+
+    page = client_request.get(
+        'main.view_notification',
+        service_id=SERVICE_ONE_ID,
+        notification_id=fake_uuid,
+    )
+
+    error_message = page.find('p', class_='notification-status-cancelled').text
+    assert normalize_spaces(error_message) == \
+           "Validation failed because this letter is 11 pages long.Letters must be 10 pages or "\
+           "less (5 double-sided sheets of paper)."
+
+
 def test_should_show_preview_error_image_letter_notification_on_preview_error(
     logged_in_client,
     fake_uuid,