diff --git a/.ds.baseline b/.ds.baseline
index 4ea306d6e..e82c0fc0e 100644
--- a/.ds.baseline
+++ b/.ds.baseline
@@ -295,7 +295,7 @@
         "filename": "tests/app/service/test_rest.py",
         "hashed_secret": "5baa61e4c9b93f3f0682250b6cf8331b7ee68fd8",
         "is_verified": false,
-        "line_number": 1288,
+        "line_number": 1290,
         "is_secret": false
       }
     ],
@@ -374,5 +374,5 @@
       }
     ]
   },
-  "generated_at": "2025-09-05T01:27:41Z"
+  "generated_at": "2025-09-11T16:22:46Z"
 }
diff --git a/tests/app/job/test_rest.py b/tests/app/job/test_rest.py
index a1092fc10..e3acfbd36 100644
--- a/tests/app/job/test_rest.py
+++ b/tests/app/job/test_rest.py
@@ -80,7 +80,7 @@ uuid_str_strategy = st.one_of(
 
 
 @pytest.mark.usefixtures("client", "sample_scheduled_job")
-@settings(max_examples=5)
+@settings(max_examples=10)
 @given(fuzzed_job_id=uuid_str_strategy, fuzzed_service_id=uuid_str_strategy)
 def test_fuzz_cancel_job(fuzzed_job_id, fuzzed_service_id, request):
     client = request.getfixturevalue("client")
diff --git a/tests/app/notifications/test_rest.py b/tests/app/notifications/test_rest.py
index 13b23b4ce..28384b1d1 100644
--- a/tests/app/notifications/test_rest.py
+++ b/tests/app/notifications/test_rest.py
@@ -19,45 +19,43 @@ from tests.app.db import create_api_key, create_notification
 @pytest.mark.usefixtures(
     "client", "sample_service", "sample_template", "notify_db_session"
 )
+@settings(max_examples=10)
+@given(
+    fuzzed_email_address=st.emails(),
+    fuzzed_personalisation=st.dictionaries(
+        keys=st.text(min_size=1, max_size=20),
+        values=st.text(min_size=0, max_size=100),
+        max_size=5,
+    ),
+    fuzzed_reference=st.one_of(st.none(), st.text(min_size=0, max_size=50)),
+)
 def test_fuzz_send_email_notification(
     client,
     sample_service,
     sample_template,
     notify_db_session,
     sample_email_notification,
+    fuzzed_email_address,
+    fuzzed_personalisation,
+    fuzzed_reference,
 ):
-    @settings(max_examples=5)
-    @given(
-        st.emails(),
-        st.dictionaries(
-            keys=st.text(min_size=1, max_size=20),
-            values=st.text(min_size=0, max_size=100),
-            max_size=5,
-        ),
-        st.one_of(st.none(), st.text(min_size=0, max_size=50)),
+
+    template_id = str(sample_template.id)
+
+    payload = {
+        "template_id": template_id,
+        "email_address": fuzzed_email_address,
+        "personalisation": fuzzed_personalisation,
+        "reference": fuzzed_reference,
+    }
+    auth_header = create_service_authorization_header(
+        service_id=sample_email_notification.service_id
     )
-    def inner(email_address, personalisation, reference):
-
-        template_id = str(sample_template.id)
-
-        payload = {
-            "template_id": template_id,
-            "email_address": email_address,
-            "personalisation": personalisation,
-            "reference": reference,
-        }
-        auth_header = create_service_authorization_header(
-            service_id=sample_email_notification.service_id
-        )
-        response = client.post(
-            "/notifications/email", json=payload, headers=[auth_header]
-        )
-        assert response.status_code in (
-            201,
-            400,
-        ), f"Unexpected status: {response.status_code}, body: {response.json}"
-
-    inner()
+    response = client.post("/notifications/email", json=payload, headers=[auth_header])
+    assert response.status_code in (
+        201,
+        400,
+    ), f"Unexpected status: {response.status_code}, body: {response.json}"
 
 
 @pytest.mark.parametrize("type", (NotificationType.EMAIL, NotificationType.SMS))
diff --git a/tests/app/service/test_rest.py b/tests/app/service/test_rest.py
index 69cf9f56a..c3f5f160a 100644
--- a/tests/app/service/test_rest.py
+++ b/tests/app/service/test_rest.py
@@ -6,6 +6,8 @@ from unittest.mock import ANY, MagicMock, patch
 import pytest
 from flask import current_app, url_for
 from freezegun import freeze_time
+from hypothesis import given, settings
+from hypothesis import strategies as st
 from sqlalchemy import func, select
 from sqlalchemy.exc import SQLAlchemyError
 
@@ -3132,6 +3134,40 @@ def test_update_service_sms_sender(client, notify_db_session):
     assert not resp_json["is_default"]
 
 
+@pytest.mark.usefixtures("client", "notify_db_session")
+@settings(max_examples=10)
+@pytest.mark.parametrize("client", [True], indirect=True)
+@given(sms_sender=st.text(min_size=0, max_size=50), is_default=st.booleans())
+def test_fuzz_update_service_sms_sender(
+    client, notify_db_session, sms_sender, is_default
+):
+    service = create_service()
+    service_sms_sender = create_service_sms_sender(
+        service=service, sms_sender="1235", is_default=False
+    )
+    data = {
+        "sms_sender": sms_sender,
+        "is_default": is_default,
+    }
+    response = client.post(
+        f"/service/{service.id}/sms-sender/{service_sms_sender.id}",
+        data=json.dumps(data),
+        headers=[
+            ("Content-Type", "application/json"),
+            create_admin_authorization_header(),
+        ],
+    )
+    assert response.status_code in [
+        200,
+        400,
+    ], f"Unexpected status: {response.status_code}, body: {response.get_data(as_text=True)}"
+
+    if response.status_code == 200:
+        resp_json = json.loads(response.get_data(as_text=True))
+        assert resp_json["sms_sender"] == sms_sender
+        assert resp_json["is_default"] == is_default
+
+
 def test_update_service_sms_sender_switches_default(client, notify_db_session):
     service = create_service_with_defined_sms_sender(sms_sender_value="first")
     service_sms_sender = create_service_sms_sender(