diff --git a/app/schemas.py b/app/schemas.py
index f673cc7fa..dd9e0d0ae 100644
--- a/app/schemas.py
+++ b/app/schemas.py
@@ -25,8 +25,9 @@ from notifications_utils.recipients import (
 
 from app import ma
 from app import models
-from app.models import ServicePermission
+from app.models import ServicePermission, INTERNATIONAL_SMS_TYPE, SMS_TYPE
 from app.dao.permissions_dao import permission_dao
+from app.dao.service_permissions_dao import dao_fetch_service_permissions
 from app.utils import get_template_instance
 
 
@@ -180,11 +181,10 @@ class ServiceSchema(BaseSchema):
     branding = field_for(models.Service, 'branding')
     dvla_organisation = field_for(models.Service, 'dvla_organisation')
     permissions = fields.Method("service_permissions")
-    
+
     def service_permissions(self, service):
         permissions = []
 
-        from app.dao.service_permissions_dao import dao_fetch_service_permissions
         perms = dao_fetch_service_permissions(service.id)
         for p in perms:
             permission = {
@@ -216,9 +216,17 @@ class ServiceSchema(BaseSchema):
 
     @validates('permissions')
     def validate_permissions(self, value):
-        for v in [val.permission for val in value]:
-            if v not in models.SERVICE_PERMISSION_TYPES:
-                raise ValidationError("Invalid Service Permission: '{}'".format(v))
+        permissions = [v.permission for v in value]
+        for p in permissions:
+            if p not in models.SERVICE_PERMISSION_TYPES:
+                raise ValidationError("Invalid Service Permission: '{}'".format(p))
+
+        if len(set(permissions)) != len(permissions):
+            duplicates = list(set([x for x in permissions if permissions.count(x) > 1]))
+            raise ValueError('Service Permission duplicated: {}'.format(duplicates))
+
+        if INTERNATIONAL_SMS_TYPE in permissions and SMS_TYPE not in permissions:
+            raise ValueError('International SMS must have SMS enabled')
 
     @pre_load()
     def format_permissions_for_data_model(self, in_data):
diff --git a/app/service/rest.py b/app/service/rest.py
index c170420f9..de1450e09 100644
--- a/app/service/rest.py
+++ b/app/service/rest.py
@@ -129,7 +129,10 @@ def update_service(service_id):
 
     current_data = dict(service_schema.dump(fetched_service).data.items())
     current_data.update(request.get_json())
-    update_dict = service_schema.load(current_data).data
+    try:
+        update_dict = service_schema.load(current_data).data
+    except ValueError as e:
+        raise InvalidRequest(str(e), status_code=400)
     dao_update_service(update_dict)
 
     if service_going_live:
diff --git a/tests/app/service/test_rest.py b/tests/app/service/test_rest.py
index 239c833fd..223ffa033 100644
--- a/tests/app/service/test_rest.py
+++ b/tests/app/service/test_rest.py
@@ -541,6 +541,44 @@ def test_update_permissions_with_an_invalid_permission_will_raise_error(client,
     assert "Invalid Service Permission: '{}'".format(invalid_permission) in result['message']['permissions']
 
 
+def test_update_permissions_with_duplicate_permissions_will_raise_error(client, sample_service):
+    auth_header = create_authorization_header()
+
+    data = {
+        'permissions': [EMAIL_TYPE, SMS_TYPE, LETTER_TYPE, LETTER_TYPE]
+    }
+
+    resp = client.post(
+        '/service/{}'.format(sample_service.id),
+        data=json.dumps(data),
+        headers=[('Content-Type', 'application/json'), auth_header]
+    )
+    result = json.loads(resp.get_data(as_text=True))
+
+    assert resp.status_code == 400
+    assert result['result'] == 'error'
+    assert "Service Permission duplicated: ['{}']".format(LETTER_TYPE) in result['message']
+
+
+def test_update_permissions_with_international_sms_without_sms_permissions_will_raise_error(client, sample_service):
+    auth_header = create_authorization_header()
+
+    data = {
+        'permissions': [EMAIL_TYPE, INTERNATIONAL_SMS_TYPE]
+    }
+
+    resp = client.post(
+        '/service/{}'.format(sample_service.id),
+        data=json.dumps(data),
+        headers=[('Content-Type', 'application/json'), auth_header]
+    )
+    result = json.loads(resp.get_data(as_text=True))
+
+    assert resp.status_code == 400
+    assert result['result'] == 'error'
+    assert "International SMS must have SMS enabled" == result['message']
+
+
 def test_update_service_flags_can_remove_service_permissions(client, sample_service):
     auth_header = create_authorization_header()
     initial_data = {