diff --git a/plugins/kolab_tags/lib/kolab_tags_engine.php b/plugins/kolab_tags/lib/kolab_tags_engine.php
index 201b23ac..b1158fc7 100644
--- a/plugins/kolab_tags/lib/kolab_tags_engine.php
+++ b/plugins/kolab_tags/lib/kolab_tags_engine.php
@@ -93,6 +93,9 @@ class kolab_tags_engine
                 if ($this->backend->remove($uid)) {
                     $response['delete'][] = $uid;
                 }
+                else {
+                    $error = true;
+                }
             }
 
             // tags creation
@@ -100,6 +103,9 @@ class kolab_tags_engine
                 if ($tag = $this->backend->create($tag)) {
                     $response['add'][] = $this->parse_tag($tag);
                 }
+                else {
+                    $error = true;
+                }
             }
 
             // tags update
@@ -107,6 +113,9 @@ class kolab_tags_engine
                 if ($this->backend->update($tag)) {
                     $response['update'][] = $this->parse_tag($tag);
                 }
+                else {
+                    $error = true;
+                }
             }
 
             if (!empty($error)) {