diff --git a/modoboa/lib/form_utils.py b/modoboa/lib/form_utils.py
index da18fa26b..c52a94a39 100644
--- a/modoboa/lib/form_utils.py
+++ b/modoboa/lib/form_utils.py
@@ -344,17 +344,19 @@ class TabForms(object):
 #
 
 
-def is_valid_host(host):
-    """IDN compatible domain validator."""
-    host = host.encode('idna').lower()
-    if not hasattr(is_valid_host, '_re'):
-        is_valid_host._re = re.compile(
-            r'^([0-9a-z][-\w]*[0-9a-z]\.)+[a-z0-9\-]{2,15}$')
-    return bool(is_valid_host._re.match(host))
+def is_valid_hostname(hostname):
+    """Domain name validaton."""
+    if len(hostname) > 255:
+        return False
+    if hostname[-1] == ".":
+        hostname = hostname[:-1]  # strip exactly one dot from the
+                                  # right, if present
+    allowed = re.compile(r"(?!-)[A-Z\d-]{1,63}(?<!-)$", re.IGNORECASE)
+    return all(allowed.match(x) for x in hostname.split("."))
 
 
 def validate_domain_name(value):
-    if not is_valid_host(value):
+    if not is_valid_hostname(value):
         raise ValidationError(_('Enter a valid domain name'), 'invalid')