diff --git a/admin/qtx_admin.php b/admin/qtx_admin.php
index 1c92e69e..58d69bae 100644
--- a/admin/qtx_admin.php
+++ b/admin/qtx_admin.php
@@ -110,7 +110,7 @@ function qtranxf_collect_translations_posted() {
         qtranxf_clean_request( 'qtranslate-fields' );
     }
 
-    if ( defined( 'DOING_AJAX' ) && DOING_AJAX ) {
+    if ( wp_doing_ajax() ) {
         // parse variables collected as a query string in an option
         foreach ( $_REQUEST as $name => $value ) {
             if ( ! is_string( $value ) ) {
diff --git a/admin/qtx_admin_utils.php b/admin/qtx_admin_utils.php
index 8d0fb266..0068d1bc 100644
--- a/admin/qtx_admin_utils.php
+++ b/admin/qtx_admin_utils.php
@@ -317,7 +317,7 @@ function qtranxf_before_admin_bar_render() {
 
 function qtranxf_admin_the_title( $title ) {
     // For nav menus, keep the raw value as the languages are handled client-side (LSB)
-    if ( defined( 'DOING_AJAX' ) && DOING_AJAX && isset( $_REQUEST['action'] ) && $_REQUEST['action'] == 'add-menu-item' ) {
+    if ( wp_doing_ajax() && isset( $_REQUEST['action'] ) && $_REQUEST['action'] == 'add-menu-item' ) {
         // When a nav menu is being added it is first handled by AJAX, see "wp_ajax_add_menu_item" in ajax-actions.php
         // For the call to the filter "the_title", see "wp_setup_nav_menu_item" in nav-menus.php
         return $title;
diff --git a/modules/wp-seo/qwpseo-activation.php b/modules/wp-seo/qwpseo-activation.php
index 4f76ed18..ab080209 100644
--- a/modules/wp-seo/qwpseo-activation.php
+++ b/modules/wp-seo/qwpseo-activation.php
@@ -1,11 +1,11 @@
 <?php
-//if(is_admin() && !defined('DOING_AJAX')){
+//if(is_admin() && !wp_doing_ajax()){
 //	require_once(dirname(__FILE__).'/qwpseo-activation.php');
 //	$file = wp_normalize_path(__FILE__);
 //	register_activation_hook($file, 'qwpseo_activation_hook');
 //}
 
-//if(defined('DOING_AJAX')){
+//if(wp_doing_ajax()){
 //	require_once(dirname(__FILE__).'/qwpseo-activation.php');
 //	add_action('wp_ajax_qwpseo_meta_fix', 'qwpseo_ajax_meta_fix');
 //}else{
diff --git a/qtranslate_core.php b/qtranslate_core.php
index bdeeb3c9..b983bf9f 100644
--- a/qtranslate_core.php
+++ b/qtranslate_core.php
@@ -34,7 +34,7 @@ function qtranxf_init_language() {
         if ( defined( 'WP_ADMIN' ) && WP_ADMIN ) {
             $url_info['WP_ADMIN'] = true;
         }
-        if ( defined( 'DOING_AJAX' ) ) {
+        if ( wp_doing_ajax() ) {
             $url_info['DOING_AJAX_POST'] = $_POST;
         }
         if ( wp_doing_cron() ) {
@@ -166,7 +166,7 @@ function qtranxf_detect_language( &$url_info ) {
     // TODO check if we shouldn't generalize the referrer parsing to all cases, do we need all these limitations?
     $parse_referrer = qtranxf_is_rest_request_expected() ||
                       ( ( ! $lang || ! isset( $url_info['doing_front_end'] ) ) &&
-                        ( defined( 'DOING_AJAX' ) || ! $url_info['cookie_enabled'] ) );
+                        ( wp_doing_ajax() || ! $url_info['cookie_enabled'] ) );
 
     // parse language and front info from HTTP_REFERER
     if ( isset( $_SERVER['HTTP_REFERER'] ) && $parse_referrer ) {
@@ -227,7 +227,7 @@ function qtranxf_detect_language( &$url_info ) {
     $url_info['language'] = $lang;
 
     // REST calls should be deterministic (stateless), no special language detection e.g. based on cookie
-    $url_info['set_cookie'] = ! defined( 'DOING_AJAX' ) && ! qtranxf_is_rest_request_expected();
+    $url_info['set_cookie'] = ! wp_doing_ajax() && ! qtranxf_is_rest_request_expected();
 
     /**
      * Hook for possible other methods
diff --git a/qtranslate_utils.php b/qtranslate_utils.php
index d5a008d2..b75dffed 100644
--- a/qtranslate_utils.php
+++ b/qtranslate_utils.php
@@ -631,7 +631,7 @@ function qtranxf_is_rest_request_expected() {
  * @return bool
  */
 function qtranxf_can_redirect() {
-    return ! defined( 'WP_ADMIN' ) && ! defined( 'DOING_AJAX' ) && ! defined( 'WP_CLI' ) && ! wp_doing_cron() && empty( $_POST )
+    return ! defined( 'WP_ADMIN' ) && ! wp_doing_ajax() && ! defined( 'WP_CLI' ) && ! wp_doing_cron() && empty( $_POST )
            && ( ! qtranxf_is_rest_request_expected() )
            // TODO clarify: 'REDIRECT_*' needs more testing --> && !isset($_SERVER['REDIRECT_URL'])
            && ( ! isset( $_SERVER['REDIRECT_STATUS'] ) || $_SERVER['REDIRECT_STATUS'] == '200' );
@@ -1042,7 +1042,7 @@ function qtranxf_match_language_locale( $locale ) {
 }
 
 function qtranxf_get_page_referer() {
-    if ( defined( 'DOING_AJAX' ) ) {
+    if ( wp_doing_ajax() ) {
         global $q_config;
         if ( isset( $q_config['url_info']['page_referer'] ) ) {
             return $q_config['url_info']['page_referer'];