diff --git a/src/Search/Bucket.php b/src/Search/Bucket.php
index afea300..7f2c132 100644
--- a/src/Search/Bucket.php
+++ b/src/Search/Bucket.php
@@ -19,7 +19,10 @@ public function docCount(): int
         return $this->bucket['doc_count'] ?? 0;
     }
 
-    public function key(): string
+    /**
+     * @return mixed
+     */
+    public function key()
     {
         return $this->bucket['key'];
     }