diff -u b/core/modules/rest/src/Plugin/views/display/RestExport.php b/core/modules/rest/src/Plugin/views/display/RestExport.php
--- b/core/modules/rest/src/Plugin/views/display/RestExport.php
+++ b/core/modules/rest/src/Plugin/views/display/RestExport.php
@@ -284,7 +284,8 @@
     $header = [];
     $header['Content-type'] = $this->getMimeType();
 
-    $response = new CacheableResponse($this->renderer->renderRoot(SafeMarkup::set($output)), 200);
+    $output['#markup'] = SafeMarkup::set($output['#markup']);
+    $response = new CacheableResponse($this->renderer->renderRoot($output), 200);
     $cache_metadata = CacheableMetadata::createFromRenderArray($output);
 
     $response->addCacheableDependency($cache_metadata);