Title: Cannot Modify Header information
Last modified: May 15, 2021

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# Cannot Modify Header information

 *  [ShaneM](https://wordpress.org/support/users/shanem/)
 * (@shanem)
 * [5 years ago](https://wordpress.org/support/topic/cannot-modify-header-information-172/)
 * Good day,
 * The following error only seems to present itself when I hit edit page from the
   admin bar and try and update a page.
 * Cannot modify header information – headers already sent by (output started at/
   public_html/wp-includes/functions.php:4757) in /public_html/wp-includes/rest-
   api/class-wp-rest-server.php on line 1642
 * I have disabled all plugins, disabled cache CDN, and yet continue to get this
   error which, from what I can tell, is core WordPress. I have replaced all the
   files with a fresh download via FTP and am still getting it. Any help to narrow
   it down would be grateful.
 * Thank you.
    -  This topic was modified 5 years ago by [ShaneM](https://wordpress.org/support/users/shanem/).
 * The page I need help with: _[[log in](https://login.wordpress.org/?redirect_to=https%3A%2F%2Fwordpress.org%2Fsupport%2Ftopic%2Fcannot-modify-header-information-172%2F%3Foutput_format%3Dmd&locale=en_US)
   to see the link]_

Viewing 3 replies - 1 through 3 (of 3 total)

 *  Moderator [t-p](https://wordpress.org/support/users/t-p/)
 * (@t-p)
 * [5 years ago](https://wordpress.org/support/topic/cannot-modify-header-information-172/#post-14442429)
 * Try reviewing this info to solve header already sent problem: [https://wordpress.org/support/article/faq-troubleshooting/#how-do-i-solve-the-headers-already-sent-warning-problem](https://wordpress.org/support/article/faq-troubleshooting/#how-do-i-solve-the-headers-already-sent-warning-problem)
 *  Thread Starter [ShaneM](https://wordpress.org/support/users/shanem/)
 * (@shanem)
 * [5 years ago](https://wordpress.org/support/topic/cannot-modify-header-information-172/#post-14444796)
 * I’ve done all those things. The functions.php in wp-includes does not end with
   a ?>.
 * Should it?
 *  [Jack](https://wordpress.org/support/users/jdabber/)
 * (@jdabber)
 * [5 years ago](https://wordpress.org/support/topic/cannot-modify-header-information-172/#post-14445086)
 * Hi ShaneM, did you edit any PHP files recently before this error occurred? For
   example, did you do any editing in the “Editor” area under the “Appearance” tab?
 * As a note, I usually got this error when I accidentally introduced whitespace
   or a new line before the opening <?php in a *.php file I had recently edited.

Viewing 3 replies - 1 through 3 (of 3 total)

The topic ‘Cannot Modify Header information’ is closed to new replies.

## Tags

 * [functions](https://wordpress.org/support/topic-tag/functions/)
 * [header](https://wordpress.org/support/topic-tag/header/)
 * [rest](https://wordpress.org/support/topic-tag/rest/)

 * In: [Fixing WordPress](https://wordpress.org/support/forum/how-to-and-troubleshooting/)
 * 3 replies
 * 3 participants
 * Last reply from: [Jack](https://wordpress.org/support/users/jdabber/)
 * Last activity: [5 years ago](https://wordpress.org/support/topic/cannot-modify-header-information-172/#post-14445086)
 * Status: not resolved

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