Title: E_ERROR – Uncaught Error: Call to undefined function wp_is_block_theme() Last modified: March 22, 2022 --- # E_ERROR – Uncaught Error: Call to undefined function wp_is_block_theme() * Resolved [sanderstalpers](https://wordpress.org/support/users/sanderstalpers/) * (@sanderstalpers) * [4 years, 2 months ago](https://wordpress.org/support/topic/e_error-uncaught-error-call-to-undefined-function-wp_is_block_theme/) * After updating the Yoast SEO plugin to v18.4 or v18.4.1, this error occurs. As a result: – in the WP backend, the Yoast Search Appearance tab is empty. The tabs at the top are showing, but no settings are showing at all – the sitemap. xml is not correct. This includes all content types, including those that were set to hidden – as a workaround, I rolled back the plugin version to v18.2 or v18.3. This fixes the issues and things work correctly again. – WordPress sends the error report listed below: * Can you please advise how to fix this? Thanks! ======================== * From: WordPress Date: Tue, Mar 22, 2022 at 7:03 PM Subject: [Castor] Your Site is Experiencing a Technical Issue To: * Howdy! * Since WordPress 5.2 there is a built-in feature that detects when a plugin or theme causes a fatal error on your site, and notifies you with this automated email. * In this case, WordPress caught an error with one of your plugins, Yoast SEO. * First, visit your website ([https://castoredcstage.wpengine.com/](https://castoredcstage.wpengine.com/)) and check for any visible issues. Next, visit the page where the error was caught( [https://castoredcstage.wpengine.com/wp-admin/admin.php?page=wpseo_titles](https://castoredcstage.wpengine.com/wp-admin/admin.php?page=wpseo_titles)) and check for any visible issues. * Please contact your host for assistance with investigating this issue further. * If your site appears broken and you can’t access your dashboard normally, WordPress now has a special “recovery mode”. This lets you safely login to your dashboard and investigate further. * [https://castoredcstage.wpengine.com/wp-login.php?action=enter_recovery_mode&rm_token=81aN3zTOeAETfA5A0sNBWz&rm_key=BB2KvzGQiFZoQmKLPjK8Pm](https://castoredcstage.wpengine.com/wp-login.php?action=enter_recovery_mode&rm_token=81aN3zTOeAETfA5A0sNBWz&rm_key=BB2KvzGQiFZoQmKLPjK8Pm) * To keep your site safe, this link will expire in 1 day. Don’t worry about that, though: a new link will be emailed to you if the error occurs again after it expires. * When seeking help with this issue, you may be asked for some of the following information: WordPress version 5.8.3 Current theme: Castor EDC (version 3.8.0) Current plugin: Yoast SEO (version 18.4.1) PHP version 8.0.16 * Error Details ============= An error of type E_ERROR was caused in line 14 of the file /nas/content/live/castoredcstage/wp-content/plugins/wordpress-seo/admin/ views/tabs/metas/general.php. Error message: Uncaught Error: Call to undefined function wp_is_block_theme() in /nas/content/live/castoredcstage/wp-content/plugins/ wordpress-seo/admin/views/tabs/metas/general.php:14 Stack trace: #0 /nas/content/ live/castoredcstage/wp-content/plugins/wordpress-seo/admin/class-option-tabs- formatter.php(72): require() #1 /nas/content/live/castoredcstage/wp-content/plugins/ wordpress-seo/admin/class-option-tabs.php(119): WPSEO_Option_Tabs_Formatter-> run(Object(WPSEO_Option_Tabs), Object(Yoast_Form)) #2 /nas/content/live/castoredcstage/ wp-content/plugins/wordpress-seo/admin/pages/metas.php(25): WPSEO_Option_Tabs- >display(Object(Yoast_Form)) #3 /nas/content/live/castoredcstage/wp-content/plugins/ wordpress-seo/admin/menu/class-menu.php(80): require_once(‘/nas/content/li…’)# 4 /nas/content/live/castoredcstage/wp-content/plugins/wordpress-seo/admin/menu/ class-menu.php(63): WPSEO_Menu->show_page(‘wpseo_titles’) #5 /nas/content/live/ castoredcstage/wp-includes/class-wp-hook.php(303): WPSEO_Menu->load_page(”) # 6 /nas/content/live/castoredcstage/wp-includes/class-wp-hook.php(327): WP_Hook- >apply_filters(”, Array) #7 /nas/content/live/castoredcstage/wp-includes/plugin. php(470): WP_Hook->do_action(Array) #8 /nas/content/live/castoredcstage/wp-admin/ admin.php(259): do_action(‘seo_page_wpseo_…’) #9 {main} thrown Viewing 3 replies - 1 through 3 (of 3 total) * [Roman Axelrod](https://wordpress.org/support/users/romanaxeweb/) * (@romanaxeweb) * [4 years, 2 months ago](https://wordpress.org/support/topic/e_error-uncaught-error-call-to-undefined-function-wp_is_block_theme/#post-15488566) * Same here. Rollback to v18.2 fixed the issue. * [Roman Axelrod](https://wordpress.org/support/users/romanaxeweb/) * (@romanaxeweb) * [4 years, 2 months ago](https://wordpress.org/support/topic/e_error-uncaught-error-call-to-undefined-function-wp_is_block_theme/#post-15489498) * The function [wp_is_block_theme](https://developer.wordpress.org/reference/functions/wp_is_block_theme/) introduced in WordPress v5.9 and was used in Yoast v18.3: [https://github.com/Yoast/wordpress-seo/commit/26d29e8c0cb19b0825d89f0fc1d861c75b27e556](https://github.com/Yoast/wordpress-seo/commit/26d29e8c0cb19b0825d89f0fc1d861c75b27e556) * Means the Yoast v18.3 is not compatible with 5.8.3 that we are still using. * Obviously, the best solution is to update the WordPress core to latest version. - This reply was modified 4 years, 2 months ago by [Roman Axelrod](https://wordpress.org/support/users/romanaxeweb/). * Thread Starter [sanderstalpers](https://wordpress.org/support/users/sanderstalpers/) * (@sanderstalpers) * [4 years, 2 months ago](https://wordpress.org/support/topic/e_error-uncaught-error-call-to-undefined-function-wp_is_block_theme/#post-15492650) * Thanks [@romanaxeweb](https://wordpress.org/support/users/romanaxeweb/) for the explanation and solution. Upgrading to WP 5.9.2 fixed this issue for me. Viewing 3 replies - 1 through 3 (of 3 total) The topic ‘E_ERROR – Uncaught Error: Call to undefined function wp_is_block_theme()’ is closed to new replies. * ![](https://ps.w.org/wordpress-seo/assets/icon-256x256.gif?rev=3419908) * [Yoast SEO - Advanced SEO with real-time guidance and built-in AI](https://wordpress.org/plugins/wordpress-seo/) * [Frequently Asked Questions](https://wordpress.org/plugins/wordpress-seo/#faq) * [Support Threads](https://wordpress.org/support/plugin/wordpress-seo/) * [Active Topics](https://wordpress.org/support/plugin/wordpress-seo/active/) * [Unresolved Topics](https://wordpress.org/support/plugin/wordpress-seo/unresolved/) * [Reviews](https://wordpress.org/support/plugin/wordpress-seo/reviews/) ## Tags * [Search Appearance](https://wordpress.org/support/topic-tag/search-appearance/) * [undefined error](https://wordpress.org/support/topic-tag/undefined-error/) * 3 replies * 2 participants * Last reply from: [sanderstalpers](https://wordpress.org/support/users/sanderstalpers/) * Last activity: [4 years, 2 months ago](https://wordpress.org/support/topic/e_error-uncaught-error-call-to-undefined-function-wp_is_block_theme/#post-15492650) * Status: resolved