diff --git a/antispam/forms.py b/antispam/forms.py
index a2f97124..0e327f2a 100644
--- a/antispam/forms.py
+++ b/antispam/forms.py
@@ -1,5 +1,3 @@
-import re
-
 from django import forms
 from django.core.validators import EmailValidator
 from django.utils.translation import gettext_lazy as _
@@ -7,12 +5,18 @@ from django.utils.translation import gettext_lazy as _
 from antispam.models import ToxicDomain
 
 
+class AntiSpamEmailValidator(EmailValidator):
+    def __call__(self, value: str):
+        super().__call__(value)
+        domain_part = value.rsplit("@", 1)[1]
+        if ToxicDomain.objects.filter(domain=domain_part).exists():
+            raise forms.ValidationError(_("Email domain is not allowed."))
+
+
+validate_antispam_email = AntiSpamEmailValidator()
+
+
 class AntiSpamEmailField(forms.EmailField):
     """An email field that email addresses with a known toxic domain."""
 
-    def run_validators(self, value: str):
-        super().run_validators(value)
-        # Domain part should exist since email validation is guaranteed to run first
-        domain = re.search(EmailValidator.domain_regex, value)
-        if ToxicDomain.objects.filter(domain=domain[0]).exists():
-            raise forms.ValidationError(_("Email domain is not allowed."))
+    default_validators = [validate_antispam_email]
diff --git a/core/tests/test_core.py b/core/tests/test_core.py
index 930e8819..964b7823 100644
--- a/core/tests/test_core.py
+++ b/core/tests/test_core.py
@@ -100,8 +100,9 @@ class TestUserRegistration:
         payload = valid_payload | payload_edit
         response = client.post(reverse("core:register"), payload)
         assert response.status_code == 200
-        error_html = f'<ul class="errorlist"><li>{expected_error}</li></ul>'
-        assertInHTML(error_html, str(response.content.decode()))
+        errors = BeautifulSoup(response.text, "lxml").find_all(class_="errorlist")
+        assert len(errors) == 1
+        assert errors[0].text == expected_error
         assert not User.objects.filter(email=payload["email"]).exists()
 
     def test_register_honeypot_fail(self, client: Client, valid_payload):