diff --git a/src/third_party/mozjs-45/mfbt/tests/TestMacroArgs.cpp b/src/third_party/mozjs-45/mfbt/tests/TestMacroArgs.cpp
new file mode 100644
index 0000000..0d97604
--- /dev/null
+++ b/src/third_party/mozjs-45/mfbt/tests/TestMacroArgs.cpp
@@ -0,0 +1,31 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/MacroArgs.h"
+
+MOZ_STATIC_ASSERT_VALID_ARG_COUNT(1);
+MOZ_STATIC_ASSERT_VALID_ARG_COUNT(1, 2);
+
+static_assert(MOZ_PASTE_PREFIX_AND_ARG_COUNT(100, a, b, c) == 1003, "");
+
+static_assert(MOZ_PASTE_PREFIX_AND_ARG_COUNT(, a, b, c) == 3, "");
+static_assert(MOZ_PASTE_PREFIX_AND_ARG_COUNT(, a) == 1, "");
+static_assert(MOZ_PASTE_PREFIX_AND_ARG_COUNT(, !a) == 1, "");
+static_assert(MOZ_PASTE_PREFIX_AND_ARG_COUNT(, (a, b)) == 1, "");
+
+static_assert(MOZ_PASTE_PREFIX_AND_ARG_COUNT(, MOZ_ARGS_AFTER_1(a, b, c)) == 2,
+              "MOZ_ARGS_AFTER_1(a, b, c) should expand to 'b, c'");
+static_assert(MOZ_ARGS_AFTER_2(a, b, 3) == 3,
+              "MOZ_ARGS_AFTER_2(a, b, 3) should expand to '3'");
+
+static_assert(MOZ_ARG_1(10, 20, 30) == 10, "");
+static_assert(MOZ_ARG_2(10, 20, 30) == 20, "");
+
+int
+main()
+{
+  return 0;
+}