--- a/js/src/jsapi-tests/moz.build
+++ b/js/src/jsapi-tests/moz.build
@@ -108,16 +108,17 @@ UNIFIED_SOURCES += [
     'testThreadingThread.cpp',
     'testToSignedOrUnsignedInteger.cpp',
     'testTypedArrays.cpp',
     'testUbiNode.cpp',
     'testUncaughtSymbol.cpp',
     'testUTF8.cpp',
     'testWasmLEB128.cpp',
     'testWeakMap.cpp',
+    'testWindowNonConfigurable.cpp',
     'testXDR.cpp',
 ]
 
 SOURCES += [
     # There are clashing definitions of js::jit::AssemblerBuffer.
     'testAssemblerBuffer.cpp',
 ]
 

new file mode 100644
--- /dev/null
+++ b/js/src/jsapi-tests/testWindowNonConfigurable.cpp
@@ -0,0 +1,54 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ */
+/* 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 "jsapi-tests/tests.h"
+
+static bool
+windowProxy_defineProperty(JSContext* cx, JS::HandleObject obj, JS::HandleId id,
+                           JS::Handle<JS::PropertyDescriptor> desc,
+                           JS::ObjectOpResult& result)
+{
+    if (desc.hasConfigurable() && !desc.configurable()) {
+        result.failCantDefineWindowNonConfigurable();
+        return true;
+    }
+
+    return NativeDefineProperty(cx, obj.as<js::NativeObject>(), id, desc, result);
+}
+
+static const js::ObjectOps windowProxy_objectOps = {
+    nullptr,
+    windowProxy_defineProperty
+};
+
+static const js::Class windowProxy_class = {
+    "WindowProxy",
+    0,
+    nullptr,
+    nullptr,
+    nullptr,
+    &windowProxy_objectOps
+};
+
+BEGIN_TEST(testWindowNonConfigurable)
+{
+    JS::RootedObject obj(cx, JS_NewObject(cx, Jsvalify(&windowProxy_class)));
+    CHECK(obj);
+    CHECK(JS_DefineProperty(cx, global, "windowProxy", obj, 0));
+    JS::RootedValue v(cx);
+    EVAL("Object.defineProperty(windowProxy, 'bar', {value: 1, configurable: false})", &v);
+    CHECK(v.isFalse()); // This is the important bit!
+    EVAL("Object.defineProperty(windowProxy, 'bar', {value: 1, configurable: true})", &v);
+    CHECK(&v.toObject() == obj);
+    EVAL("Reflect.defineProperty(windowProxy, 'foo', {value: 1, configurable: false})", &v);
+    CHECK(v.isFalse());
+    EVAL("Reflect.defineProperty(windowProxy, 'foo', {value: 1, configurable: true})", &v);
+    CHECK(v.isTrue());
+
+    return true;
+}
+END_TEST(testWindowNonConfigurable)