diff --git a/core/modules/outside_in/js/outside_in.js b/core/modules/outside_in/js/outside_in.js
index 715106e..7eb241c 100644
--- a/core/modules/outside_in/js/outside_in.js
+++ b/core/modules/outside_in/js/outside_in.js
@@ -243,7 +243,7 @@
           if (instance.hasOwnProperty('dialogType')) {
             instance.options.url = instance.options.url.replace(searchLink, replaceLink);
             // Check to make sure existing dialogOptions aren't overridden.
-            if (!('dialogOptions' in instance.options.data)) {
+            if (!instance.options.data.hasOwnProperty('dialogOptions')) {
               instance.options.data.dialogOptions = {};
             }
             instance.options.data.dialogOptions.outsideInActiveEditableId = $(instance.element).parents('.outside-in-editable').attr('id');
diff --git a/core/modules/outside_in/outside_in.libraries.yml b/core/modules/outside_in/outside_in.libraries.yml
index 5c9fc8e..faa314a 100644
--- a/core/modules/outside_in/outside_in.libraries.yml
+++ b/core/modules/outside_in/outside_in.libraries.yml
@@ -21,6 +21,7 @@ drupal.outside_in:
     - core/jquery.once
     - core/drupal.ajax
     - core/drupalSettings
+    - core/jquery.form
 drupal.off_canvas:
   version: VERSION
   js:
diff --git a/core/modules/outside_in/src/Render/MainContent/OffCanvasRender.php b/core/modules/outside_in/src/Render/MainContent/OffCanvasRender.php
index 9536215..acc4012 100644
--- a/core/modules/outside_in/src/Render/MainContent/OffCanvasRender.php
+++ b/core/modules/outside_in/src/Render/MainContent/OffCanvasRender.php
@@ -42,11 +42,13 @@ public function renderResponse(array $main_content, Request $request, RouteMatch
     $response = new AjaxResponse();
 
     // Add place holder form messages from Ajax form requests.
-    $main_content['off_canvas_messages'] = [
-      '#type' => 'container',
-      '#attributes' => ['class' => ['messages__wrapper']],
-      '#weight' => -100,
-    ];
+    $main_content = [
+      'off_canvas_messages' => [
+        '#type' => 'container',
+        '#attributes' => ['class' => ['messages__wrapper']],
+        '#weight' => 100,
+      ],
+    ] + $main_content;
 
     // First render the main content, because it might provide a title.
     $content = $this->renderer->renderRoot($main_content);
diff --git a/core/modules/outside_in/tests/src/FunctionalJavascript/OffCanvasTest.php b/core/modules/outside_in/tests/src/FunctionalJavascript/OffCanvasTest.php
index 8fe8f74..b2cb676 100644
--- a/core/modules/outside_in/tests/src/FunctionalJavascript/OffCanvasTest.php
+++ b/core/modules/outside_in/tests/src/FunctionalJavascript/OffCanvasTest.php
@@ -107,13 +107,15 @@ public function testNarrowWidth() {
    * Test form errors in the Off-Canvas dialog.
    */
   public function testFormErrors() {
+    $web_assert = $this->assertSession();
     $this->drupalGet('/offcanvas-test-links');
     $page = $this->getSession()->getPage();
     $page->clickLink('Show form!');
     $this->waitForOffCanvasToOpen();
+    $web_assert->elementExists('css', '.messages__wrapper');
     $page->pressButton('Invalid');
-    $this->assertSession()->assertWaitOnAjaxRequest();
-    $this->assertSession()->elementContains('css', '#drupal-offcanvas', 'Validation error');
+    $web_assert->assertWaitOnAjaxRequest();
+    $web_assert->elementContains('css', '#drupal-offcanvas', 'Validation error');
   }
 
 }