diff --git a/tests/app/dao/test_organisation_dao.py b/tests/app/dao/test_organisation_dao.py
index 45cf5f589..eeb254616 100644
--- a/tests/app/dao/test_organisation_dao.py
+++ b/tests/app/dao/test_organisation_dao.py
@@ -90,10 +90,6 @@ def test_update_organisation(notify_db_session):
     (['ABC', 'DEF'], {'abc', 'def'}),
     ([], set()),
     (None, {'123', '456'}),
-    pytest.param(
-        ['abc', 'ABC'], {'abc'},
-        marks=pytest.mark.xfail(raises=IntegrityError)
-    ),
 ))
 def test_update_organisation_domains_lowercases(
     notify_db_session,
@@ -113,6 +109,29 @@ def test_update_organisation_domains_lowercases(
     assert {domain.domain for domain in organisation.domains} == expected_domains
 
 
+@pytest.mark.parametrize('domain_list, expected_domains', (
+        (['abc', 'ABC'], {'abc'}),
+))
+def test_update_organisation_domains_lowercases_integrity_error(
+    notify_db_session,
+    domain_list,
+    expected_domains,
+):
+    create_organisation()
+
+    organisation = Organisation.query.one()
+
+    # Seed some domains
+    dao_update_organisation(organisation.id, domains=['123', '456'])
+
+    with pytest.raises(expected_exception=IntegrityError):
+
+        # This should overwrite the seeded domains
+        dao_update_organisation(organisation.id, domains=domain_list)
+
+        assert {domain.domain for domain in organisation.domains} == expected_domains
+
+
 def test_update_organisation_does_not_update_the_service_if_certain_attributes_not_provided(
     sample_service,
     sample_organisation,
diff --git a/tests/app/organisation/test_rest.py b/tests/app/organisation/test_rest.py
index 3fcd47d1f..40de5aafa 100644
--- a/tests/app/organisation/test_rest.py
+++ b/tests/app/organisation/test_rest.py
@@ -127,10 +127,7 @@ def test_get_organisation_by_id_returns_domains(admin_request, notify_db_session
     ('foo.gov.uk', 200),
     ('bar.gov.uk', 200),
     ('oof.gov.uk', 404),
-    pytest.param(
-        'rab.gov.uk', 200,
-        marks=pytest.mark.xfail(raises=AssertionError),
-    ),
+    ('rab.gov.uk', 200),
     (None, 400),
     ('personally.identifying.information@example.com', 400),
 ))
@@ -152,7 +149,9 @@ def test_get_organisation_by_domain(
         domain=domain,
     )
 
-    if expected_status == 200:
+    if domain == 'rab.gov.uk' and expected_status == 200:
+        assert response['id'] == str(other_org.id)
+    elif expected_status == 200:
         assert response['id'] == str(org.id)
     else:
         assert response['result'] == 'error'