--- a/testing/web-platform/tests/tools/webdriver/webdriver/client.py
+++ b/testing/web-platform/tests/tools/webdriver/webdriver/client.py
@@ -263,17 +263,17 @@ class Window(object):
         """Gets the window position as a tuple of `(x, y)`."""
         rect = self.rect
         return (rect["x"], rect["y"])
 
     @position.setter
     @command
     def position(self, new_position):
         """Set window position by passing a tuple of `(x, y)`."""
-        data = x, y
+        x, y = new_position
         body = {"x": x, "y": y}
         self.session.send_session_command("POST", "window/rect", body)
 
     @property
     @command
     def state(self):
         return self.rect["state"]