diff --git a/core/misc/ajax.es6.js b/core/misc/ajax.es6.js
index a746ac70f4..942a526c0b 100644
--- a/core/misc/ajax.es6.js
+++ b/core/misc/ajax.es6.js
@@ -403,18 +403,18 @@ function loadAjaxBehavior(base) {
     this.instanceIndex = false;
 
     // @todo Remove support for 'wrapper' and solely use 'wrapper_selector'.
-    if (this.wrapper) {
+    if (this.wrapper && !this.wrapper_selector) {
+      /**
+       * @type {string}
+       */
+      this.wrapper_selector = `#${this.wrapper}`;
+
       /**
        * @deprecated Use this.wrapper_selector.
        *
        * @type {string}
        */
-      this.wrapper = null;
-
-      /**
-       * @type {string}
-       */
-      this.wrapper_selector = `#${this.wrapper}`;
+      this.wrapper = this.wrapper_selector;
     }
 
     /**
diff --git a/core/misc/ajax.js b/core/misc/ajax.js
index b6f4395420..29cb346b50 100644
--- a/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -172,10 +172,10 @@ function loadAjaxBehavior(base) {
 
     this.instanceIndex = false;
 
-    if (this.wrapper) {
-      this.wrapper = null;
-
+    if (this.wrapper && !this.wrapper_selector) {
       this.wrapper_selector = '#' + this.wrapper;
+
+      this.wrapper = this.wrapper_selector;
     }
 
     this.element = element;
diff --git a/core/tests/Drupal/Tests/Core/Render/Element/RenderElementTest.php b/core/tests/Drupal/Tests/Core/Render/Element/RenderElementTest.php
index 118fe56cd0..95bc711954 100644
--- a/core/tests/Drupal/Tests/Core/Render/Element/RenderElementTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/Element/RenderElementTest.php
@@ -45,6 +45,8 @@ protected function setUp() {
   /**
    * @covers ::preRenderAjaxForm
    * @dataProvider providerTestPreRenderAjaxForm
+   *
+   * @legacy
    */
   public function testPreRenderAjaxForm($element, $expected, $url) {
     $request = Request::create('/test');