Hi Resteasy users, [ apologies for the re-post, sent from wrong email the first time ] I'm a happy user of Resteasy + Jackson for Json processing. Recently, I had the misfortune of attempting to serialize a basic String: client.post(Entity.json("Test")); if you call Jackson directly, it does the right thing: mapper.writeValueAsString("Test") => "\"Test\"" However, much to my surprise, when sending it via JAX-RS client, it is written as a bare word without quotes -- and is rejected server-side. After some debugging, I realized that both StringTextStar and JacksonJsonProvider were ending up with Priorities.USER and being seen as equivalent. No good! So I changed my registration: context.register(new JacksonJsonProvider(myMapper), Integer.MAX_VALUE); I then proceeded to triumphantly ... observe the same test failure as before! Dug quite a bit further in, and it seems that the selection process in MediaTypeMap$TypedEntryComparator has the unfortunate property that it will select (via compareTypes) a *less priority* MessageBodyWriter if the type is a tighter bound on the Entity. So in my case, I get StringTextStar -> String.class@5000 JacksonJsonProvider -> Object.class(a)Integer.MAX_VALUE and the TypedEntryComparator selects StringTextStar since String is-assignable to Object, despite my attempt at an ultimate priority registration. How do I fix this? Preferably without removing StringTextStar entirely, as I'm sure that will break something else (reading error messages perhaps). Thanks for any advice, Steven