diff --git a/locales/de/LC_MESSAGES/loops.mo b/locales/de/LC_MESSAGES/loops.mo
index 2d67f48..1e54dfb 100644
Binary files a/locales/de/LC_MESSAGES/loops.mo and b/locales/de/LC_MESSAGES/loops.mo differ
diff --git a/locales/de/LC_MESSAGES/loops.po b/locales/de/LC_MESSAGES/loops.po
index 5c3bd65..c475e64 100644
--- a/locales/de/LC_MESSAGES/loops.po
+++ b/locales/de/LC_MESSAGES/loops.po
@@ -3,7 +3,7 @@ msgstr ""
 
 "Project-Id-Version: 0.13.1\n"
 "POT-Creation-Date: 2007-05-22 12:00 CET\n"
-"PO-Revision-Date: 2015-09-22 12:00 CET\n"
+"PO-Revision-Date: 2015-10-25 12:00 CET\n"
 "Last-Translator: Helmut Merz <helmutm@cy55.de>\n"
 "Language-Team: loops developers <helmutm@cy55.de>\n"
 "MIME-Version: 1.0\n"
@@ -855,6 +855,9 @@ msgstr "Benutzer registrieren"
 msgid "Register new member"
 msgstr "Neu registrieren"
 
+msgid "Login name not allowed."
+msgstr "Die von Ihnen eingegebene Benutzerkennung enthält Sonderzeichen, z. B. Umlaute."
+
 msgid "Login name already taken."
 msgstr "Die von Ihnen eingegebene Benutzerkennung ist schon vergeben."
 
diff --git a/organize/browser/member.py b/organize/browser/member.py
index 7aabe80..bf6e0b7 100644
--- a/organize/browser/member.py
+++ b/organize/browser/member.py
@@ -1,5 +1,5 @@
 #
-#  Copyright (c) 2014 Helmut Merz helmutm@cy55.de
+#  Copyright (c) 2015 Helmut Merz helmutm@cy55.de
 #
 #  This program is free software; you can redistribute it and/or modify
 #  it under the terms of the GNU General Public License as published by
@@ -91,6 +91,7 @@ class BaseMemberRegistration(NodeView):
     formErrors = dict(
         confirm_nomatch=FormError(_(u'Password and password confirmation '
                                     u'do not match.')),
+        illegal_loginname=FormError(_('Login name not allowed.')),
         duplicate_loginname=FormError(_('Login name already taken.')),
     )
 
diff --git a/organize/member.py b/organize/member.py
index ab2aded..42f1c0a 100644
--- a/organize/member.py
+++ b/organize/member.py
@@ -1,5 +1,5 @@
 #
-#  Copyright (c) 2013 Helmut Merz helmutm@cy55.de
+#  Copyright (c) 2015 Helmut Merz helmutm@cy55.de
 #
 #  This program is free software; you can redistribute it and/or modify
 #  it under the terms of the GNU General Public License as published by
@@ -79,8 +79,10 @@ class MemberRegistrationManager(object):
         if pfName is None:
             pfName = options(self.principalfolder_key,
                              (self.default_principalfolder,))[0]
-        self.createPrincipal(pfName, userId, password, lastName, firstName, 
-                             useExisting=useExisting)
+        rc = self.createPrincipal(pfName, userId, password, 
+                         lastName, firstName, useExisting=useExisting)
+        if rc is not None:
+            return rc
         if not groups:
             groups = options(self.groups_key, ())
         self.setGroupsForPrincipal(pfName, userId,  groups=groups)
@@ -90,6 +92,8 @@ class MemberRegistrationManager(object):
     def createPrincipal(self, pfName, userId, password, lastName,
                               firstName=u'', groups=[], useExisting=False,
                               overwrite=False, **kw):
+        if not self.checkPrincipalId(userId):
+            return dict(fieldName='loginName', error='illegal_loginname')            
         pFolder = getPrincipalFolder(self.context, pfName)
         if IPersonBasedAuthenticator.providedBy(pFolder):
              pFolder.setPassword(userId, password)
@@ -123,10 +127,18 @@ class MemberRegistrationManager(object):
             if gFolder is not None:
                 group = gFolder.get(gName)
                 if group is not None:
-                    members = list(group.principals)
+                    members = [p for p in group.principals 
+                                 if self.checkPrincipalId(p)]
                     members.append(pFolder.prefix + userId)
                     group.principals = members
 
+    def checkPrincipalId(self, pid):
+        try:
+            pid = str(pid)
+            return True
+        except UnicodeEncodeError:
+            return False
+
     def createPersonForPrincipal(self, pfName, userId, lastName, firstName=u'',
                                  useExisting=False, **kw):
         concepts = self.context.getConceptManager()