CreateResponse method in asp.net Web API

calling this method:

public HttpResponseMessage PostProduct(Product item)
{
    item = repository.Add(item);
    var response = this.Request.CreateResponse<Product>CreateResponse(HttpStatusCode.Created, item);

    string uri = Url.RouteUrl("DefaultApi", new { id = item.Id });
    response.Headers.Location = new Uri(uri);
    return response;
}

Is causing a compile-time error:

'System.Web.HttpRequestBase' does not contain a definition for 'CreateResponse' and the
            best extension method overload 'System.Net.Http.HttpRequestMessageExtensions.CreateResponse<T>
(System.Net.Http.HttpRequestMessage, System.Net.HttpStatusCode, T)' has some invalid arguments.

What am I missing here?