diff --git a/app/main/forms.py b/app/main/forms.py
index 177e8ac0d..19cc8498f 100644
--- a/app/main/forms.py
+++ b/app/main/forms.py
@@ -1563,7 +1563,7 @@ class ServiceReplyToEmailForm(StripWhitespaceForm):
 
 
 class ServiceSmsSenderForm(StripWhitespaceForm):
-    sms_sender = StringField(
+    sms_sender = GovukTextInputField(
         'Text message sender',
         validators=[
             DataRequired(message="Cannot be empty"),
diff --git a/app/templates/views/service-settings/sms-sender/add.html b/app/templates/views/service-settings/sms-sender/add.html
index 1bf80bacb..2760a6b95 100644
--- a/app/templates/views/service-settings/sms-sender/add.html
+++ b/app/templates/views/service-settings/sms-sender/add.html
@@ -16,11 +16,10 @@
   ) }}
 
   {% call form_wrapper() %}
-    {{ textbox(
-      form.sms_sender,
-      width='1-4',
-      hint='Up to 11 characters, letters, numbers and spaces only'
-    ) }}
+    {{ form.sms_sender(param_extensions={
+      "classes": "govuk-!-width-one-quarter",
+      "hint": {"text": "Up to 11 characters, letters, numbers and spaces only"}
+    }) }}
     {% if not first_sms_sender %}
       {{ form.is_default }}
     {% endif %}
diff --git a/app/templates/views/service-settings/sms-sender/edit.html b/app/templates/views/service-settings/sms-sender/edit.html
index 67889fcd2..181e24db8 100644
--- a/app/templates/views/service-settings/sms-sender/edit.html
+++ b/app/templates/views/service-settings/sms-sender/edit.html
@@ -22,11 +22,10 @@
         <span class="hint"> This phone number receives replies and cannot be changed </span>
       </p>
     {% else %}
-      {{ textbox(
-        form.sms_sender,
-        width='1-4',
-        hint='Up to 11 characters, letters, numbers and spaces only'
-      ) }}
+      {{ form.sms_sender(param_extensions={
+        "classes": "govuk-!-width-one-quarter",
+        "hint": {"text": "Up to 11 characters, letters, numbers and spaces only"}
+      }) }}
     {% endif %}
     {% if form.is_default.data %}
       <p class="form-group">
diff --git a/tests/app/main/views/test_service_settings.py b/tests/app/main/views/test_service_settings.py
index 93a8b4cb0..bce5407e5 100644
--- a/tests/app/main/views/test_service_settings.py
+++ b/tests/app/main/views/test_service_settings.py
@@ -2285,14 +2285,14 @@ def test_incorrect_sms_sender_input(
         _expected_status=(200 if expected_error else 302)
     )
 
-    error_message = page.select_one('.error-message')
+    error_message = page.select_one('.govuk-error-message')
     count_of_api_calls = len(mock_add_sms_sender.call_args_list)
 
     if not expected_error:
         assert not error_message
         assert count_of_api_calls == 1
     else:
-        assert normalize_spaces(error_message.text) == expected_error
+        assert expected_error in error_message.text
         assert count_of_api_calls == 0