diff --git a/src/Config.php b/src/Config.php
index 54996b7..c43bc50 100644
--- a/src/Config.php
+++ b/src/Config.php
@@ -343,7 +343,7 @@ public function offsetUnset($offset)
      * @param  Config $merge
      * @return Config
      */
-    public function merge(self $merge)
+    public function merge(Config $merge)
     {
         /** @var Config $value */
         foreach ($merge as $key => $value) {