diff --git a/src/openklant/accounts/migrations/0003_user_filled_email_unique.py b/src/openklant/accounts/migrations/0003_user_filled_email_unique.py
new file mode 100644
index 00000000..f4d043c6
--- /dev/null
+++ b/src/openklant/accounts/migrations/0003_user_filled_email_unique.py
@@ -0,0 +1,21 @@
+# Generated by Django 4.2.11 on 2024-07-02 14:30
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("accounts", "0002_auto_20211116_0918"),
+    ]
+
+    operations = [
+        migrations.AddConstraint(
+            model_name="user",
+            constraint=models.UniqueConstraint(
+                condition=models.Q(("email", ""), _negated=True),
+                fields=("email",),
+                name="filled_email_unique",
+            ),
+        ),
+    ]
diff --git a/src/openklant/accounts/models.py b/src/openklant/accounts/models.py
index f67dc0e5..7b2e2b9c 100644
--- a/src/openklant/accounts/models.py
+++ b/src/openklant/accounts/models.py
@@ -1,6 +1,7 @@
 from django.contrib.auth.models import AbstractBaseUser, PermissionsMixin
 from django.contrib.auth.validators import UnicodeUsernameValidator
 from django.db import models
+from django.db.models import Q
 from django.utils import timezone
 from django.utils.translation import gettext_lazy as _
 
@@ -52,6 +53,11 @@ class User(AbstractBaseUser, PermissionsMixin):
     class Meta:
         verbose_name = _("user")
         verbose_name_plural = _("users")
+        constraints = [
+            models.UniqueConstraint(
+                fields=["email"], condition=~Q(email=""), name="filled_email_unique"
+            )
+        ]
 
     def get_full_name(self):
         """
diff --git a/src/openklant/accounts/tests/test_user_manager.py b/src/openklant/accounts/tests/test_user_manager.py
index 1a6ab7d2..b3a9d154 100644
--- a/src/openklant/accounts/tests/test_user_manager.py
+++ b/src/openklant/accounts/tests/test_user_manager.py
@@ -1,3 +1,4 @@
+from django.db import IntegrityError
 from django.test import TestCase
 
 from ..models import User
@@ -20,3 +21,16 @@ def test_create_user(self):
         self.assertFalse(user.is_superuser)
         self.assertFalse(user.is_staff)
         self.assertFalse(user.has_usable_password())
+
+    def test_create_users_with_same_email(self):
+        User.objects.create(username="AAA", email="aaa@aaa.aaa", password="aaa!")
+
+        with self.assertRaises(IntegrityError):
+            User.objects.create(username="BBB", email="aaa@aaa.aaa", password="bbb!")
+
+    def test_create_user_with_blank_emails(self):
+        User.objects.create(username="AAA", email="", password="aaa!")
+        User.objects.create(username="BBB", email="", password="bbb!")
+
+        self.assertEqual(User.objects.count(), 2)
+