diff --git a/probe_scraper/probe_expiry_alert.py b/probe_scraper/probe_expiry_alert.py
index 98dffb37..4459ea9a 100644
--- a/probe_scraper/probe_expiry_alert.py
+++ b/probe_scraper/probe_expiry_alert.py
@@ -287,8 +287,9 @@ def check_bugzilla_user_exists(email: str, api_key: str):
     try:
         user_response.raise_for_status()
     except requests.exceptions.HTTPError as e:
-        # 400 is raised if user does not exist
-        if e.response.status_code == 400 and e.response.json()["code"] == 51:
+        # Error code 51 means the user does not exist. Bugzilla used to return
+        # it with HTTP 400 and now returns it with HTTP 404.
+        if e.response.status_code in (400, 404) and e.response.json()["code"] == 51:
             return False
         raise
     # As of Sept 2020, api seems to be returning 200 response with an unknown
diff --git a/tests/test_probe_expiry_alert.py b/tests/test_probe_expiry_alert.py
index b47b346f..7ec4bcf6 100644
--- a/tests/test_probe_expiry_alert.py
+++ b/tests/test_probe_expiry_alert.py
@@ -3,6 +3,7 @@
 from dataclasses import dataclass
 from unittest import mock
 
+import pytest
 from requests.exceptions import HTTPError
 
 from probe_scraper import probe_expiry_alert
@@ -493,10 +494,11 @@ def test_get_longest_prefix():
     assert probe_expiry_alert.get_longest_prefix(["abc"]) == "abc"
 
 
+@pytest.mark.parametrize("status_code", [400, 404])
 @mock.patch("requests.get")
-def test_check_bugzilla_user_account_not_found(mock_get):
+def test_check_bugzilla_user_account_not_found(mock_get, status_code):
     mock_response = mock.MagicMock()
-    mock_response.status_code = 400
+    mock_response.status_code = status_code
     mock_response.json = mock.MagicMock(return_value={"code": 51})
 
     def user_not_found():