diff --git a/lib/WebDriver/Session.php b/lib/WebDriver/Session.php
index c8825ee..f149b8d 100644
--- a/lib/WebDriver/Session.php
+++ b/lib/WebDriver/Session.php
@@ -335,7 +335,7 @@ public function focusWindow($handle)
     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);