diff --git a/composer.json b/composer.json
index 4cbc3f0..372d1f9 100644
--- a/composer.json
+++ b/composer.json
@@ -10,7 +10,7 @@
         }
     ],
     "require": {
-        "guzzlehttp/guzzle": "^6.3|^7.0",
+        "guzzlehttp/guzzle": "^7.0",
         "PHP": "^7.1",
         "kornrunner/keccak": "~1.0",
         "phpseclib/phpseclib": "~2.0.11",
diff --git a/src/Contract.php b/src/Contract.php
index 87ad1fc..25843f4 100644
--- a/src/Contract.php
+++ b/src/Contract.php
@@ -587,6 +587,8 @@ class Contract
             $method = array_splice($arguments, 0, 1)[0];
             $callback = array_pop($arguments);
 
+            $arguments = is_array($arguments[0]) ? $arguments[0] : $arguments;
+            
             if (!is_string($method)) {
                 throw new InvalidArgumentException('Please make sure the method is string.');
             }