diff --git a/plugins/tasklist/drivers/kolab/tasklist_kolab_driver.php b/plugins/tasklist/drivers/kolab/tasklist_kolab_driver.php
index 042b9989..556fdc72 100644
--- a/plugins/tasklist/drivers/kolab/tasklist_kolab_driver.php
+++ b/plugins/tasklist/drivers/kolab/tasklist_kolab_driver.php
@@ -1365,7 +1365,7 @@ class tasklist_kolab_driver extends tasklist_driver
             rcube::raise_error(array(
                 'code' => 600, 'type' => 'php',
                 'file' => __FILE__, 'line' => __LINE__,
-                'message' => "Invalid list identifer to save task: " . var_dump($list_id, true)),
+                'message' => "Invalid list identifer to save task: " . print_r($list_id, true)),
                 true, false);
             return false;
         }