diff --git a/tests/test_LdapCherry.py b/tests/test_LdapCherry.py
index 1c5066a..69445bc 100644
--- a/tests/test_LdapCherry.py
+++ b/tests/test_LdapCherry.py
@@ -98,6 +98,7 @@ def _is_html_error(line):
                 r'.*Warning: <input> attribute "id" has invalid value.*',
                 r'.*Warning: <a> proprietary attribute.*',
                 r'.*Warning: <input> attribute "type" has invalid value.*',
+                r'.*Warning: <span> proprietary attribute.*',
              ]:
         if re.match(p, line):
             return False