# Request header field Dont-Chunk is not allowed by Access-Control-Allow-Headers in preflight response
**URL:** https://meta.discourse.org/t/request-header-field-dont-chunk-is-not-allowed-by-access-control-allow-headers-in-preflight-response/49469
**Category:** Bug
**Created:** [August 31, 2016, 2:51am UTC](https://meta.discourse.org/t/request-header-field-dont-chunk-is-not-allowed-by-access-control-allow-headers-in-preflight-response/49469 "2016-08-31T02:51:39Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@brahn](https://meta.discourse.org/u/brahn)
#### Post date: [August 31, 2016, 2:51am UTC](https://meta.discourse.org/t/request-header-field-dont-chunk-is-not-allowed-by-access-control-allow-headers-in-preflight-response/49469/1 "2016-08-31T02:51:39Z")
After setting up [Full site CDN acceleration for Discourse](https://meta.discourse.org/t/full-site-cdn-acceleration-for-discourse/21467) I am seeing the following in chrome console:
> XMLHttpRequest cannot load [https://mydomain.com/message-bus/d487d3e56113405b95d297fbc468c99d/poll?dlp=t](https://mydomain.com/message-bus/d487d3e56113405b95d297fbc468c99d/poll?dlp=t). Request header field Dont-Chunk is not allowed by Access-Control-Allow-Headers in preflight response.
Also, it doesn’t seem to always happen and it seems to be only those requests with the `?dip=t` parameter:
The site is on stable, v1.6.1 and I am assuming that something in my config is not quite right but I am not sure where to start.
Any hints on where to look or how to approach diagnosing this?
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### Author:  [@sam](https://meta.discourse.org/u/sam)
#### Post date: [August 31, 2016, 2:53am UTC](https://meta.discourse.org/t/request-header-field-dont-chunk-is-not-allowed-by-access-control-allow-headers-in-preflight-response/49469/2 "2016-08-31T02:53:06Z")
Interesting, this is actually a but in our Access control process
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### Author:  [@sam](https://meta.discourse.org/u/sam)
#### Post date: [August 31, 2016, 2:57am UTC](https://meta.discourse.org/t/request-header-field-dont-chunk-is-not-allowed-by-access-control-allow-headers-in-preflight-response/49469/3 "2016-08-31T02:57:39Z")
Can you try:
[https://github.com/discourse/discourse/commit/50379183e1deb6c3fae4b17ec46b96d1a18180c1](https://github.com/discourse/discourse/commit/50379183e1deb6c3fae4b17ec46b96d1a18180c1)
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### Author:  [@brahn](https://meta.discourse.org/u/brahn)
#### Post date: [August 31, 2016, 3:00am UTC](https://meta.discourse.org/t/request-header-field-dont-chunk-is-not-allowed-by-access-control-allow-headers-in-preflight-response/49469/4 "2016-08-31T03:00:37Z")
Thanks @sam
Can I push that into the rails app within the container somehow, just for testing, or is the only way to rebuild on the development branch?
Edit: I entered the app, edited this file and restart unicorn. That sound about right? Testing now…
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### Author:  [@brahn](https://meta.discourse.org/u/brahn)
#### Post date: [August 31, 2016, 3:37am UTC](https://meta.discourse.org/t/request-header-field-dont-chunk-is-not-allowed-by-access-control-allow-headers-in-preflight-response/49469/5 "2016-08-31T03:37:10Z")
This appears to be working for me now. Many thanks!
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### Author:  [@sam](https://meta.discourse.org/u/sam)
#### Post date: [August 31, 2016, 3:37am UTC](https://meta.discourse.org/t/request-header-field-dont-chunk-is-not-allowed-by-access-control-allow-headers-in-preflight-response/49469/6 "2016-08-31T03:37:51Z")