diff --git a/lib/kolab_sync_storage.php b/lib/kolab_sync_storage.php
--- a/lib/kolab_sync_storage.php
+++ b/lib/kolab_sync_storage.php
@@ -1969,8 +1969,9 @@
             );
 
             if ($row = $db->fetch_assoc()) {
-                $synctime = $row['synctime'];
-                // @TODO: make sure synctime from sql is in "Y-m-d H:i:s" format
+                // MariaDB's datetime output includes microseconds, we need to remove them,
+                // it must be "Y-m-d H:i:s" format
+                $synctime = preg_match('/\.[0-9]+/', '', $row['synctime']);
                 $this->relations[$folderid][$synctime] = json_decode($row['data'], true);
             }