diff --git a/library/Zend/Mail/Storage/Abstract.php b/library/Zend/Mail/Storage/Abstract.php
index d96da2c742..8e555764fb 100644
--- a/library/Zend/Mail/Storage/Abstract.php
+++ b/library/Zend/Mail/Storage/Abstract.php
@@ -215,7 +215,7 @@ abstract public function getNumberByUniqueId($id);
      *
      * @return   int
      */
-     public function count()
+     public function count(): int
      {
         return $this->countMessages();
      }