diff --git a/adserver/auth/migrations/0011_alter_useradvertisermember_unique_together.py b/adserver/auth/migrations/0011_alter_useradvertisermember_unique_together.py
new file mode 100644
index 00000000..fc40684f
--- /dev/null
+++ b/adserver/auth/migrations/0011_alter_useradvertisermember_unique_together.py
@@ -0,0 +1,18 @@
+# Generated by Django 5.2.7 on 2025-11-01 16:57
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('adserver', '0104_auto_renew_payment_method'),
+        ('adserver_auth', '0010_data_all_emails_verified'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='useradvertisermember',
+            unique_together={('user', 'advertiser')},
+        ),
+    ]
diff --git a/adserver/auth/models.py b/adserver/auth/models.py
index b7cf224b..8ee67e8c 100644
--- a/adserver/auth/models.py
+++ b/adserver/auth/models.py
@@ -255,6 +255,8 @@ class Meta:
         # To do that, we needed to start with the same table
         db_table = "adserver_auth_user_advertisers"
 
+        unique_together = ("user", "advertiser")
+
 
 class UserPublisherMember(models.Model):
     """User-Publisher 'through' model."""
diff --git a/adserver/tests/test_advertiser_dashboard.py b/adserver/tests/test_advertiser_dashboard.py
index bf4f40ab..1e68f03d 100644
--- a/adserver/tests/test_advertiser_dashboard.py
+++ b/adserver/tests/test_advertiser_dashboard.py
@@ -1252,6 +1252,7 @@ def test_authorized_users_invite_existing(self):
         self.assertContains(response, "Successfully invited")
         self.assertEqual(User.objects.filter(email=email).count(), 1)
         self.assertEqual(User.objects.filter(name=name).count(), 1)
+        self.assertEqual(UserAdvertiserMember.objects.filter(advertiser=self.advertiser, user__email=email).count(), 1)
 
         # The 2nd request didn't create a user or update the user's name
         self.assertEqual(User.objects.filter(name="Yet Another User").count(), 0)
diff --git a/adserver/views.py b/adserver/views.py
index 6acdfd04..05dc1e24 100644
--- a/adserver/views.py
+++ b/adserver/views.py
@@ -1857,13 +1857,16 @@ def dispatch(self, request, *args, **kwargs):
     def form_valid(self, form):
         result = super().form_valid(form)
 
-        # Add m2m and role
-        role = form.cleaned_data["role"]
-        UserAdvertiserMember.objects.create(
-            advertiser=self.advertiser,
-            user=self.object,
-            role=role,
-        )
+        if not UserAdvertiserMember.objects.filter(
+            advertiser=self.advertiser, user=self.object
+        ).exists():
+            # Add m2m and role
+            role = form.cleaned_data["role"]
+            UserAdvertiserMember.objects.create(
+                advertiser=self.advertiser,
+                user=self.object,
+                role=role,
+            )
 
         messages.success(
             self.request,