Faking method with dynamic params

Greetings!
I'm getting an odd "Destination array was not long enough." ArgumentException when I fake a method that has the params keyword. A snippet is worth a thousand words, so observe:

    public class FakeMe
    {
        public string Params(string firstArg, params object[] otherArgs)
        {
            return "I'm real!";
        }
    }

    [TestFixture]
    [Isolated]
    public class Test
    {
        [Test]
        public void Test_Params()
        {
            var fake = Isolate.Fake.Instance<FakeMe>();
            const string iMFake = "I'm fake!";
            Isolate.WhenCalled((string firstArg) => fake.Params(firstArg, "")).AndArgumentsMatch(firstArg => firstArg == "lolwut") .WillReturn(iMFake);

            var result = fake.Params("lolwut");

            Assert.AreEqual(iMFake, result);
        }
    }

Note that the exception occurs on the Isolate.WhenCalled line.

What am I doing wrong?
Thanks!