CORS errors with Flask and gevent

I have an API running, using Flask, Flask-SQLAlchemy, and Flask-Restless, and am trying to make POST/PUT/DELETE requests from javascript (backbone.js, to be precise). However, I keep running into CORS errors - everything except GET returns an HTTP OPTIONS 501 Not Implemented Error in the browser. Initially, I tried adding the least restrictive CORS headers possible to all responses: ``` @app.after_request def after(response): response.headers.add('Access-Control-Allow-Origin', '*') response.headers.add('Access-Control-Allow-Methods', 'POST, GET, PUT, PATCH, DELETE, OPTIONS') response.headers.add('Access-Control-Allow-Headers', 'Content-Type, X-Requested-With') response.headers.add('Access-Control-Max-Age', '1728000') return response ``` CORS seemed to fail when the request's Content-Type header was set to application/json (as required by the API), so a quick hack was made to get things working: ``` @app.before_request def before(): request.environ['CONTENT_TYPE'] = 'application/json' ``` However, everything except POST still fails. Also, gevent's logging is turned on, but no OPTIONS requests are ever logged (which I believe is the CORS preflight stuff), even when the browser shows them failing with a 501. Do I need to change something in gevent or Flask to get CORS working? Edit: Running the API using the built-in Flask server works, so gevent is the problem here, but I can't seem to find much in the way of docs...