diff --git a/app/models.py b/app/models.py
index cf58a6867..5df7730bf 100644
--- a/app/models.py
+++ b/app/models.py
@@ -1193,7 +1193,7 @@ class Notification(db.Model):
     postage = db.Column(db.String, nullable=True)
     CheckConstraint("""
         CASE WHEN notification_type = 'letter' THEN
-            postage in ('first', 'second')
+            postage is not null and postage in ('first', 'second')
         ELSE
             postage is null
         END
@@ -1453,7 +1453,7 @@ class NotificationHistory(db.Model, HistoryModel):
     postage = db.Column(db.String, nullable=True)
     CheckConstraint("""
         CASE WHEN notification_type = 'letter' THEN
-            postage in ('first', 'second')
+            postage is not null and postage in ('first', 'second')
         ELSE
             postage is null
         END
diff --git a/migrations/versions/0230_noti_postage_constraint.py b/migrations/versions/0230_noti_postage_constraint.py
index 118d51b39..a8c40d7ec 100644
--- a/migrations/versions/0230_noti_postage_constraint.py
+++ b/migrations/versions/0230_noti_postage_constraint.py
@@ -17,7 +17,7 @@ def upgrade():
         ALTER TABLE notifications ADD CONSTRAINT "chk_notifications_postage_null"
         CHECK (
             CASE WHEN notification_type = 'letter' THEN
-                postage in ('first', 'second')
+                postage is not null and postage in ('first', 'second')
             ELSE
                 postage is null
             END
@@ -28,7 +28,7 @@ def upgrade():
         ALTER TABLE notification_history ADD CONSTRAINT "chk_notification_history_postage_null"
         CHECK (
             CASE WHEN notification_type = 'letter' THEN
-                postage in ('first', 'second')
+                postage is not null and postage in ('first', 'second')
             ELSE
                 postage is null
             END