diff --git a/lib/Doctrine/Common/Collections/Collection.php b/lib/Doctrine/Common/Collections/Collection.php
index d27b3b568..b4100e242 100644
--- a/lib/Doctrine/Common/Collections/Collection.php
+++ b/lib/Doctrine/Common/Collections/Collection.php
@@ -178,9 +178,9 @@ public function last();
     /**
      * Gets the key/index of the element at the current iterator position.
      *
-     * @return int|string
+     * @return int|string|null
      *
-     * @psalm-return TKey
+     * @psalm-return TKey|null
      */
     public function key();