diff --git a/base/univention-system-setup/umc/python/setup/util.py b/base/univention-system-setup/umc/python/setup/util.py
index 624a9ed334..51ddacc7c0 100644
--- a/base/univention-system-setup/umc/python/setup/util.py
+++ b/base/univention-system-setup/umc/python/setup/util.py
@@ -870,22 +870,15 @@ def is_domainname(domainname):
 is_domainname.RE = re.compile(r'^[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?$', re.I)
 
 
-def is_windowsdomainname(domainname):
-	return is_windowsdomainname.RE.match(domainname) is not None and len(domainname) < 14
-
-
-is_windowsdomainname.RE = re.compile(r"^[A-Z](?:[A-Z0-9-]*[A-Z0-9])?$")
+def is_windowsdomainname(name):
+	validname = re.sub('[\\\\/:*?><|.]', '', name)
+	return name == validname and len(name) < 14
 
 
 def domain2windowdomain(domainname):
 	windomain = domainname.split('.', 1)[0].upper()
 
-	invalidChars = re.compile(r"^[^A-Z]*([A-Z0-9-]*?)[^A-Z0-9]*$")
-	match = invalidChars.match(windomain)
-	if match:
-		windomain = match.group(1)
-	else:
-		windomain = ''
+	windomain = re.sub('[\\\\/:*?><|.]', '', windomain)
 
 	windomain = windomain[:15]  # enforce netbios limit