diff --git a/management/univention-directory-manager-modules/modules/univention/admin/syntax.py b/management/univention-directory-manager-modules/modules/univention/admin/syntax.py
index ba336ed..0fc9e04 100644
--- a/management/univention-directory-manager-modules/modules/univention/admin/syntax.py
+++ b/management/univention-directory-manager-modules/modules/univention/admin/syntax.py
@@ -1237,6 +1237,13 @@ class reverseLookupSubnet(simple):
 	regex = re.compile(r'^((%s)|(%s))$' % (regex_IPv4, regex_IPv6, ))
 	error_message = _('A subnet for reverse lookup consists of the first one to three parts of an IPv4 address (example: "192.168.0") or of the first 1 to 31 nibbles of an IPv6 address with leading zeroes and without :: substitution (example: "2001:0db8:010")')
 
+	@classmethod
+	def parse(cls, text):
+		text = super(reverseLookupSubnet, cls).parse(text)
+		if text in ('0', '127', '255'):
+			raise univention.admin.uexceptions.valueError(_("The subnets 0, 127 and 255 are preserved."))
+		return text
+
 class reverseLookupZoneName(simple):
 	#                       <-    IPv6 reverse zone   -> <-                           IPv4 reverse zone                           ->
 	#                       nibble dot-separated ...arpa   <-                      0-255                     -> dot-separated .arpa