diff --git a/app/models.py b/app/models.py
index 498240b2c..6eeda9a77 100644
--- a/app/models.py
+++ b/app/models.py
@@ -226,7 +226,7 @@ class Service(db.Model, Versioned):
     email_from = db.Column(db.Text, index=False, unique=True, nullable=False)
     created_by = db.relationship('User')
     created_by_id = db.Column(UUID(as_uuid=True), db.ForeignKey('users.id'), index=True, nullable=False)
-    prefix_sms = db.Column(db.Boolean, nullable=True, default=True)
+    prefix_sms = db.Column(db.Boolean, nullable=False, default=True)
     organisation_id = db.Column(UUID(as_uuid=True), db.ForeignKey('organisation.id'), index=True, nullable=True)
     organisation = db.relationship('Organisation')
     dvla_organisation_id = db.Column(