The Amazon Fire TV set-top box just got a lot more worthwhile for people wanting to add HBO to TVs without getting additional cable boxes. That is, unless you’re a Comcast customer.

Amazon announced today that HBO Go is now available for the Fire TV box and will be coming to the less-expensive, recently released Fire TV stick sometime this spring.

While this still requires that you have a basic cable subscription and a subscription to HBO (or that you have someone willing to lend you their login info), it can be a money-saver for people with multi-TV homes who don’t feel like paying the cable company for additional cable boxes.

Perhaps that’s why not every cable provider is on board yet. According to the HBO Go/Fire TV activation page, most of the major pay-TV players — DirecTV, Dish, Time Warner Cable, Cox, Verizon FiOS, AT&T U-Verse — are allowing customers to stream HBO Go this way, there are two huge omissions: Comcast and Charter.

Because you have have to use your pay-TV operator’s login info to access HBO Go, it’s up to each provider to determine which devices you’re allowed to watch the service on. As many a Roku buyer has learned over the years, not every provider is too eager to let people get a free add-on service that may take away the ancillary revenue of additional set-top boxes or lead to cord-cutting when HBO finally releases its long-awaited standalone streaming option.