Please re-evaluate; the current behaviour is incompatible with JSON specification in favour of providing the user/application/consumer of the resulted JSON information regarding the conversion process. Given what is stated in the documentation I do agree with the default behaviour, but I don't agree with only supporting "most JavaScript based encoders and decoders" and not supporting the JSON specification. I would opt to support "most encoders and decoders" + the JSON specification. Furthermore, the allow_nan doesn't allow anything, it forces as no alternative is provided. Setting it to false does not make it disallow, but makes it not work at all, forcing to use the default behaviour. I would suggest when allow_nan is set to false, to make it compliant with JSON and use null instead (as per specification). This way we are supporting most Javascript based encoders and decoders, but can also produce JSON compliant output.