diff --git a/lib/Kolab/CalDAV/Calendar.php b/lib/Kolab/CalDAV/Calendar.php
--- a/lib/Kolab/CalDAV/Calendar.php
+++ b/lib/Kolab/CalDAV/Calendar.php
@@ -85,7 +85,7 @@
     {
         // return ACL information based on IMAP MYRIGHTS
         $rights = $this->storage->get_myrights();
-        if ($rights && !PEAR::isError($rights)) {
+        if ($rights && !is_a($rights, 'PEAR_Error')) {
             // user has at least read access to calendar folders listed
             $acl = array(
                 array(
diff --git a/lib/Kolab/CardDAV/AddressBook.php b/lib/Kolab/CardDAV/AddressBook.php
--- a/lib/Kolab/CardDAV/AddressBook.php
+++ b/lib/Kolab/CardDAV/AddressBook.php
@@ -120,7 +120,7 @@
     {
         // return ACL information based on IMAP MYRIGHTS
         $rights = $this->storage ? $this->storage->get_myrights() : null;
-        if ($rights && !PEAR::isError($rights)) {
+        if ($rights && !is_a($rights, 'PEAR_Error')) {
             // user has at least read access to calendar folders listed
             $acl = array(
                 array(