diff --git a/src/Pay/LegacySignature.php b/src/Pay/LegacySignature.php
index aa588435a..a9d2843f5 100644
--- a/src/Pay/LegacySignature.php
+++ b/src/Pay/LegacySignature.php
@@ -57,8 +57,6 @@ public function sign(array $params): array
             $signType = 'md5';
         }
 
-        unset($params['sign_type']);
-
         $sign = call_user_func_array($signType, [urldecode(http_build_query($attributes))]);
 
         if (! is_string($sign)) {