diff --git a/src/EntityListeners/TreeCacheInvalidationListener.php b/src/EntityListeners/TreeCacheInvalidationListener.php
index e18e936d..79a6aab2 100644
--- a/src/EntityListeners/TreeCacheInvalidationListener.php
+++ b/src/EntityListeners/TreeCacheInvalidationListener.php
@@ -36,6 +36,7 @@ use App\Entity\Base\DBElement;
 use App\Entity\Base\StructuralDBElement;
 use App\Entity\UserSystem\Group;
 use App\Entity\UserSystem\User;
+use App\Services\UserCacheKeyGenerator;
 use Doctrine\ORM\Event\LifecycleEventArgs;
 use Doctrine\ORM\Event\PostFlushEventArgs;
 use Doctrine\ORM\Event\PreFlushEventArgs;
@@ -45,10 +46,12 @@ use Symfony\Contracts\Cache\TagAwareCacheInterface;
 class TreeCacheInvalidationListener
 {
     protected $cache;
+    protected $keyGenerator;
 
-    public function __construct(TagAwareCacheInterface $treeCache)
+    public function __construct(TagAwareCacheInterface $treeCache, UserCacheKeyGenerator $keyGenerator)
     {
         $this->cache = $treeCache;
+        $this->keyGenerator = $keyGenerator;
     }
 
     /**
@@ -69,7 +72,7 @@ class TreeCacheInvalidationListener
 
         //If a user change, then invalidate all cached trees for him
         if ($element instanceof User) {
-            $tag = "user_" . $element->getUsername();
+            $tag = $this->keyGenerator->generateKey($element);
             $this->cache->invalidateTags([$tag]);
         }
 
diff --git a/src/Services/ToolsTreeBuilder.php b/src/Services/ToolsTreeBuilder.php
index b0efce04..bfc7e414 100644
--- a/src/Services/ToolsTreeBuilder.php
+++ b/src/Services/ToolsTreeBuilder.php
@@ -45,17 +45,18 @@ class ToolsTreeBuilder
 
     protected $translator;
     protected $urlGenerator;
-    protected $security;
+    protected $keyGenerator;
     protected $cache;
 
     public function __construct(TranslatorInterface $translator, UrlGeneratorInterface $urlGenerator,
-                                TagAwareCacheInterface $treeCache, Security $security)
+                                TagAwareCacheInterface $treeCache, UserCacheKeyGenerator $keyGenerator)
     {
         $this->translator = $translator;
         $this->urlGenerator = $urlGenerator;
 
-        $this->security = $security;
         $this->cache = $treeCache;
+
+        $this->keyGenerator = $keyGenerator;
     }
 
     /**
@@ -65,13 +66,11 @@ class ToolsTreeBuilder
      */
     public function getTree() : array
     {
-        $username = $this->security->getUser()->getUsername();
+        $key = "tree_tools_" .  $this->keyGenerator->generateKey();
 
-        $key = "tree_tools_" .  $username;
-
-        return $this->cache->get($key, function (ItemInterface $item) use ($username) {
+        return $this->cache->get($key, function (ItemInterface $item) {
             //Invalidate tree, whenever group or the user changes
-            $item->tag(["tree_tools", "groups", "user_" . $username]);
+            $item->tag(["tree_tools", "groups", $this->keyGenerator->generateKey()]);
 
             $tree = array();
             $tree[] = new TreeViewNode($this->translator->trans('tree.tools.edit'), null, $this->getEditNodes());
diff --git a/src/Services/TreeBuilder.php b/src/Services/TreeBuilder.php
index dadf2c24..a5ea2c95 100644
--- a/src/Services/TreeBuilder.php
+++ b/src/Services/TreeBuilder.php
@@ -60,15 +60,15 @@ class TreeBuilder
     protected $em;
     protected $translator;
     protected $cache;
-    protected $security;
+    protected $keyGenerator;
 
     public function __construct(EntityURLGenerator $URLGenerator, EntityManagerInterface $em,
-                                TranslatorInterface $translator, TagAwareCacheInterface $treeCache, Security $security)
+                                TranslatorInterface $translator, TagAwareCacheInterface $treeCache, UserCacheKeyGenerator $keyGenerator)
     {
         $this->url_generator = $URLGenerator;
         $this->em = $em;
         $this->translator = $translator;
-        $this->security = $security;
+        $this->keyGenerator = $keyGenerator;
         $this->cache = $treeCache;
     }
 
@@ -174,15 +174,14 @@ class TreeBuilder
      */
     public function typeToNodesList(string $class_name, ?StructuralDBElement $parent = null): array
     {
-        $username = $this->security->getUser()->getUsername();
         $parent_id = $parent != null ? $parent->getID() : "0";
         // Backslashes are not allowed in cache keys
         $secure_class_name = str_replace("\\", '_', $class_name);
-        $key = "list_" . $username . "_" . $secure_class_name . $parent_id;
+        $key = "list_" . $this->keyGenerator->generateKey() . "_" . $secure_class_name . $parent_id;
 
-        $ret = $this->cache->get($key, function (ItemInterface $item) use ($class_name, $parent, $secure_class_name, $username) {
+        $ret = $this->cache->get($key, function (ItemInterface $item) use ($class_name, $parent, $secure_class_name) {
             // Invalidate when groups, a element with the class or the user changes
-            $item->tag(['groups', 'tree_list', 'user_' . $username, $secure_class_name]);
+            $item->tag(['groups', 'tree_list', $this->keyGenerator->generateKey(), $secure_class_name]);
             /**
              * @var $repo StructuralDBElementRepository
              */
diff --git a/src/Services/UserCacheKeyGenerator.php b/src/Services/UserCacheKeyGenerator.php
new file mode 100644
index 00000000..5582ae91
--- /dev/null
+++ b/src/Services/UserCacheKeyGenerator.php
@@ -0,0 +1,73 @@
+<?php
+/**
+ *
+ * part-db version 0.1
+ * Copyright (C) 2005 Christoph Lechner
+ * http://www.cl-projects.de/
+ *
+ * part-db version 0.2+
+ * Copyright (C) 2009 K. Jacobs and others (see authors.php)
+ * http://code.google.com/p/part-db/
+ *
+ * Part-DB Version 0.4+
+ * Copyright (C) 2016 - 2019 Jan Böhmer
+ * https://github.com/jbtronics
+ *
+ * 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 the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
+ *
+ */
+
+namespace App\Services;
+
+
+use App\Entity\UserSystem\User;
+use Symfony\Component\Security\Core\Security;
+
+/**
+ * Purpose of this service is to generate a key unique for a user, to use in Cache keys and tags.
+ * @package App\Services
+ */
+class UserCacheKeyGenerator
+{
+    protected $security;
+
+    public function __construct(Security $security)
+    {
+        $this->security = $security;
+    }
+
+    /**
+     * Generates a key for the given user.
+     * @param User|null $user The user for which the key should be generated. When set to null, the currently logged in
+     * user is used.
+     * @return string
+     */
+    public function generateKey(User $user = null) : string
+    {
+        //If no user was specified, use the currently used one.
+        if ($user === null) {
+            $user = $this->security->getUser();
+        }
+
+        //If the user is null, then treat it as anonymous user.
+        //When the anonymous user is passed as user then use this path too.
+        if ($user === null || $user->getID() === User::ID_ANONYMOUS) {
+            return 'user$_' . User::ID_ANONYMOUS;
+        }
+
+        //In the most cases we can just use the username (its unique)
+        return "user_" . $user->getUsername();
+    }
+}
\ No newline at end of file