JMockit mocking System.currentTimeMillis()

Running this test:

@Test
public void testSystemCurrentTimeMillis() {
    new NonStrictExpectations(System.class) {{
        System.currentTimeMillis(); result = 1438357206679L;
    }};
    long currentTime = System.currentTimeMillis();
    assertEquals(1438357206679L, currentTime);
}

I get an IllegalStateException:

java.lang.IllegalStateException: Missing invocation to mocked type at this point; please make sure such invocations appear only after the declaration of a suitable mock field or parameter
    at unittests.DateTest$1.(DateTest.java:24)
    at unittests.DateTest.testSystemCurrentTimeMillis(DateTest.java:23)

What's wrong with my Test (JMockit 1.18)?