--- a/testing/marionette/harness/marionette/tests/unit/test_set_window_size.py
+++ b/testing/marionette/harness/marionette/tests/unit/test_set_window_size.py
@@ -50,17 +50,17 @@ class TestSetWindowSize(MarionetteTestCa
         size = self.marionette.set_window_size(width, height)
         self.assertIsNotNone(size, "Response is None")
         self.assertEqual(size['width'], width,
                          "New width is %s but should be %s" % (size['width'], width))
         self.assertEqual(size['height'], height,
                          "New height is %s but should be %s" % (size['height'], height))
 
     def test_possible_to_request_window_larger_than_screen(self):
-        self.marionette.set_window_size(100000, 100000)
+        self.marionette.set_window_size(4 * self.max_width, 4 * self.max_height)
         size = self.marionette.window_size
 
         # In X the window size may be greater than the bounds of the screen
         self.assertGreaterEqual(size["width"], self.max_width)
         self.assertGreaterEqual(size["height"], self.max_height)
 
     def test_that_we_can_maximise_the_window(self):
         # valid size