diff --git a/lib/WebDriver/Session.php b/lib/WebDriver/Session.php
index f8c4506..c10e855 100644
--- a/lib/WebDriver/Session.php
+++ b/lib/WebDriver/Session.php
@@ -282,7 +282,7 @@ public function focusWindow($name)
     public function frame()
     {
         if (func_num_args() === 1) {
-            $arg = func_get_arg(0); // json
+            $arg = $this->serializeArguments(func_get_arg(0)); // json
 
             $this->curl('POST', '/frame', $arg);