diff --git a/core/lib/Drupal/Core/EventSubscriber/MaintenanceModeSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/MaintenanceModeSubscriber.php
index 0af47876e7..0f8283184f 100644
--- a/core/lib/Drupal/Core/EventSubscriber/MaintenanceModeSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/MaintenanceModeSubscriber.php
@@ -127,15 +127,23 @@ public function onKernelRequestMaintenance(RequestEvent $event) {
         $this->eventDispatcher->dispatch($event, MaintenanceModeEvents::MAINTENANCE_MODE_REQUEST);
       }
       else {
-        // Display a message if the logged in user has access to the site in
-        // maintenance mode. However, suppress it on the maintenance mode
-        // settings page.
+        // Display a message if the logged-in user has access to the site in
+        // maintenance mode. Don't show maintenance message:
+        // - on AJAX requests.
+        // - on Iframe uploads.
+        // - on the maintenance mode settings page.
         if ($route_match->getRouteName() != 'system.site_maintenance_mode') {
-          if ($this->account->hasPermission('administer site configuration')) {
-            $this->messenger->addMessage($this->t('Operating in maintenance mode. <a href=":url">Go online.</a>', [':url' => $this->urlGenerator->generate('system.site_maintenance_mode')]), 'status', FALSE);
-          }
-          else {
-            $this->messenger->addMessage($this->t('Operating in maintenance mode.'), 'status', FALSE);
+          $show_message = $route_match->getRouteName() != 'system.site_maintenance_mode' &&
+            !$event->getRequest()->isXmlHttpRequest() &&
+            $event->getRequest()->get('ajax_iframe_upload', FALSE) === FALSE;
+
+          if ($show_message) {
+            if ($this->account->hasPermission('administer site configuration')) {
+              $this->messenger->addMessage($this->t('Operating in maintenance mode. <a href=":url">Go online.</a>', [':url' => $this->urlGenerator->generate('system.site_maintenance_mode')]), 'status', FALSE);
+            }
+            else {
+              $this->messenger->addMessage($this->t('Operating in maintenance mode.'), 'status', FALSE);
+            }
           }
         }
       }
diff --git a/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetTest.php b/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetTest.php
index cc4a03cee0..432cbc3e6a 100644
--- a/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetTest.php
+++ b/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetTest.php
@@ -46,6 +46,7 @@ protected function setUp(): void {
       'access content',
       'access administration pages',
       'administer site configuration',
+      'access site in maintenance mode',
       'administer users',
       'administer permissions',
       'administer content types',
@@ -140,6 +141,14 @@ public function testSingleValuedWidget() {
     $type_name = 'article';
     $field_name = 'test_file_field_1';
     $cardinality = 1;
+
+    // Turn on maintenance mode.
+    $edit = [
+      'maintenance_mode' => 1,
+    ];
+    $this->drupalGet('admin/config/development/maintenance');
+    $this->submitForm($edit, 'Save configuration');
+
     $this->createFileField($field_name, 'node', $type_name, ['cardinality' => $cardinality]);
 
     $page = $this->getSession()->getPage();
@@ -162,6 +171,10 @@ public function testSingleValuedWidget() {
     $page->attachFileToField('files[' . $field_name . '_0]', $test_file_path);
     $remove_button = $assert_session->waitForElementVisible('css', '[name="' . $field_name . '_0_remove_button"]');
     $this->assertNotNull($remove_button);
+
+    $this->assertSession()->assertWaitOnAjaxRequest();
+    $this->assertSession()->pageTextContainsOnce('Operating in maintenance mode');
+
     $page->pressButton('Save');
     $page->hasContent($test_file->name);