Mocking HttpWebRequest Accept with Moq

I'm using Moq to mock a HttpWebRequest. I'm able to mock Headers & Method but it blows up when I try to mock Accept.

Code is:

 Mock<HttpWebResponse> response = new Mock<HttpWebResponse>(MockBehavior.Loose); Mock<HttpWebRequest> request = new Mock<HttpWebRequest>(); request.Setup(s => s.GetResponse()).Returns(response.Object); request.Setup(m => m.Method).Returns("GET"); request.Setup(h => h.Accept).Returns("application/x-protobuf"); 

Exception is:

 System.NotSupportedException was unhandled by user code HResult=-2146233067 Message=Invalid setup on a non-virtual (overridable in VB) member: h => h.Accept Source=Moq StackTrace: at Moq.Mock.ThrowIfCantOverride(Expression setup, MethodInfo method) at Moq.Mock.<>c__DisplayClass1f`2.<SetupGet>b__1e() at Moq.PexProtector.Invoke[T](Func`1 function) at Moq.Mock.SetupGet[T,TProperty](Mock mock, Expression`1 expression, Func`1 condition) at Moq.Mock.<>c__DisplayClass1c`2.<Setup>b__1b() at Moq.PexProtector.Invoke[T](Func`1 function) at Moq.Mock.Setup[T,TResult](Mock mock, Expression`1 expression, Func`1 condition) at Moq.Mock`1.Setup[TResult](Expression`1 expression) at HarmonyTests.MockWebRequestCreate.CreateTestRequest(Stream protobuf)