diff --git a/plugins/libkolab/lib/kolab_storage_dataset.php b/plugins/libkolab/lib/kolab_storage_dataset.php
index 17e66de1..d23ba690 100644
--- a/plugins/libkolab/lib/kolab_storage_dataset.php
+++ b/plugins/libkolab/lib/kolab_storage_dataset.php
@@ -24,7 +24,7 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
-class kolab_storage_dataset implements Iterator, ArrayAccess
+class kolab_storage_dataset implements Iterator, ArrayAccess, Countable
 {
     private $cache;  // kolab_storage_cache instance to use for fetching data
     private $memlimit = 0;
@@ -50,6 +50,14 @@ class kolab_storage_dataset implements Iterator, ArrayAccess
     }
 
 
+    /*** Implement PHP Countable interface ***/
+
+    public function count()
+    {
+        return count($this->index);
+    }
+
+
     /*** Implement PHP ArrayAccess interface ***/
 
     public function offsetSet($offset, $value)