diff --git a/plugins/libkolab/lib/kolab_storage_cache.php b/plugins/libkolab/lib/kolab_storage_cache.php
index 0a50f7fe..c3e88da8 100644
--- a/plugins/libkolab/lib/kolab_storage_cache.php
+++ b/plugins/libkolab/lib/kolab_storage_cache.php
@@ -196,6 +196,10 @@ class kolab_storage_cache
      */
     public function set($msguid, $object, $foldername = null)
     {
+        if (!$msguid) {
+            return;
+        }
+
         // delegate to another cache instance
         if ($foldername && $foldername != $this->folder->name) {
             kolab_storage::get_folder($foldername)->cache->set($msguid, $object);
diff --git a/plugins/libkolab/lib/kolab_storage_folder.php b/plugins/libkolab/lib/kolab_storage_folder.php
index 421531a0..69cd31bd 100644
--- a/plugins/libkolab/lib/kolab_storage_folder.php
+++ b/plugins/libkolab/lib/kolab_storage_folder.php
@@ -621,7 +621,7 @@ class kolab_storage_folder
         }
 
         if ($success) {
-            $this->cache->set($result, false);
+            $this->cache->set($msguid, false);
         }
 
         return $success;