diff --git a/docs/changelog.rst b/docs/changelog.rst
index b98b466..a53cc9d 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -1,6 +1,7 @@
 Changelog
 =========
 
+* :support:`-` implement domain name validation
 * :feature:`-` implement deletion of websites
 * :feature:`-` implement setup of websites
 * :support:`-` add webtasks interface
diff --git a/gnuviechadmin/domains/forms.py b/gnuviechadmin/domains/forms.py
index ba2a654..fff18cb 100644
--- a/gnuviechadmin/domains/forms.py
+++ b/gnuviechadmin/domains/forms.py
@@ -4,6 +4,8 @@ This module defines form classes for domain editing.
 """
 from __future__ import absolute_import, unicode_literals
 
+import re
+
 from django import forms
 from django.core.urlresolvers import reverse
 from django.utils.translation import ugettext as _
@@ -17,6 +19,18 @@ from crispy_forms.layout import (
 from .models import HostingDomain
 
 
+def relative_domain_validator(value):
+    """
+    This validator ensures that the given value is a valid lowercase
+    """
+    if len(value) > 254:
+        raise forms.ValidationError(
+            _('host name too long'), code='too-long')
+    allowed = re.compile(r"(?!-)[a-z\d-]{1,63}(?<!-)$")
+    if not all(allowed.match(x) for x in value.split('.')):
+        raise forms.ValidationError(_('invalid domain name'))
+
+
 class CreateHostingDomainForm(forms.ModelForm):
     """
     This form is used to create new HostingDomain instances.
@@ -29,6 +43,7 @@ class CreateHostingDomainForm(forms.ModelForm):
     def __init__(self, instance, *args, **kwargs):
         self.hosting_package = kwargs.pop('hostingpackage')
         super(CreateHostingDomainForm, self).__init__(*args, **kwargs)
+        self.fields['domain'].validators.append(relative_domain_validator)
         self.helper = FormHelper()
         self.helper.form_action = reverse(
             'create_hosting_domain', kwargs={
diff --git a/gnuviechadmin/websites/forms.py b/gnuviechadmin/websites/forms.py
index a6fca20..fa63538 100644
--- a/gnuviechadmin/websites/forms.py
+++ b/gnuviechadmin/websites/forms.py
@@ -15,6 +15,7 @@ from crispy_forms.layout import (
     Submit,
 )
 
+from domains.forms import relative_domain_validator
 from .models import Website
 
 
@@ -31,7 +32,10 @@ class AddWebsiteForm(forms.ModelForm):
         self.hosting_package = kwargs.pop('hostingpackage')
         self.hosting_domain = kwargs.pop('domain')
         super(AddWebsiteForm, self).__init__(*args, **kwargs)
-        if Website.objects.filter(wildcard=True).exists():
+        self.fields['subdomain'].validators.append(relative_domain_validator)
+        if Website.objects.filter(
+            wildcard=True, domain=self.hosting_domain
+        ).exists():
             self.fields['wildcard'].widget = forms.HiddenInput()
 
         self.helper = FormHelper()
@@ -54,6 +58,8 @@ class AddWebsiteForm(forms.ModelForm):
         ).exists():
             raise forms.ValidationError(
                 _('There is already a website for this subdomain'))
+        relative_domain_validator(
+            "{0}.{1}".format(data, self.hosting_domain.domain))
         return data
 
     def save(self, commit=True):