Is this variant of double-checked locking safe?

Question

Consider this code based on the examples on Wikipedia but note that the question isn't restricted to Java.

class Foo {
    private Helper helper;
    private int initialized = 0;
    public Helper getHelper() {
        if (initialized == 0) {
            synchronized (this) {
                if (helper == null) {
                    helper = new Helper();
                }
            }
            initialized = 1;
        }
        return helper;
    }
}

Using a separate flag which is set outside the synchronized block should fix the issue with classic double-checked locking. When initialized is set to 1, helper is guaranteed to be visible to other threads since exiting the synchronized block should provide a memory barrier. The helper == NULL check inside the synchronized block should make sure that helper isn't created twice.

Is this variant of double-checked locking safe?