diff --git a/dom/tests/mochitest/whatwg/test_postMessage_origin.xhtml b/dom/tests/mochitest/whatwg/test_postMessage_origin.xhtml
index b7a6c4478f8..6490d7e790e 100644
--- a/dom/tests/mochitest/whatwg/test_postMessage_origin.xhtml
+++ b/dom/tests/mochitest/whatwg/test_postMessage_origin.xhtml
@@ -377,6 +377,12 @@ var tests =
 
      wrongReturnOrigin: true
    },
+   // 55
+   {
+     args: ["NOT-RECEIVED", undefined],
+     source: "sameDomain",
+     code: DOMException.SYNTAX_ERR
+   },
   ];
 
 function allTests()