diff -r 000000000000 -r 6474c204b198 js/src/jsapi-tests/testOps.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jsapi-tests/testOps.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,65 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ *
+ * Tests for operators and implicit type conversion.
+ */
+/* 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
+my_convert(JSContext* context, JS::HandleObject obj, JSType type, JS::MutableHandleValue rval)
+{
+    if (type == JSTYPE_VOID || type == JSTYPE_STRING || type == JSTYPE_NUMBER || type == JSTYPE_BOOLEAN) {
+        rval.set(JS_NumberValue(123));
+        return true;
+    }
+    return false;
+}
+
+static const JSClass myClass = {
+    "MyClass",
+    0,
+    JS_PropertyStub, JS_DeletePropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
+    JS_EnumerateStub, JS_ResolveStub, my_convert
+};
+
+static bool
+createMyObject(JSContext* context, unsigned argc, jsval *vp)
+{
+    JS_BeginRequest(context);
+
+    //JS_GC(context); //<- if we make GC here, all is ok
+
+    JSObject* myObject = JS_NewObject(context, &myClass, JS::NullPtr(), JS::NullPtr());
+    *vp = OBJECT_TO_JSVAL(myObject);
+
+    JS_EndRequest(context);
+
+    return true;
+}
+
+static const JSFunctionSpec s_functions[] =
+{
+    JS_FN("createMyObject", createMyObject, 0, 0),
+    JS_FS_END
+};
+
+BEGIN_TEST(testOps_bug559006)
+{
+    CHECK(JS_DefineFunctions(cx, global, s_functions));
+
+    EXEC("function main() { while(1) return 0 + createMyObject(); }");
+
+    for (int i = 0; i < 9; i++) {
+        JS::RootedValue rval(cx);
+        CHECK(JS_CallFunctionName(cx, global, "main", JS::HandleValueArray::empty(),
+                                  &rval));
+        CHECK_SAME(rval, INT_TO_JSVAL(123));
+    }
+    return true;
+}
+END_TEST(testOps_bug559006)
+