diff -u b/core/lib/Drupal/Core/Render/RenderVariable.php b/core/lib/Drupal/Core/Render/RenderVariable.php
--- b/core/lib/Drupal/Core/Render/RenderVariable.php
+++ b/core/lib/Drupal/Core/Render/RenderVariable.php
@@ -7,21 +7,25 @@
 
 namespace Drupal\Core\Render;
 
-use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Component\Render\MarkupInterface;
 
+/**
+ * Provides helpers to generate render arrays.
+ */
 class RenderVariable {
 
   /**
    * Prefixes a render variable.
    *
-   * @param string|\Drupal\Component\Utility\SafeStringInterface|array $thing
+   * @param string|\Drupal\Component\Render\MarkupInterface|array $thing
    *   A render variable. Either a string, an object that is safe or a render
    *   array.
-   * @param string|\Drupal\Component\Utility\SafeStringInterface...
+   * @param string|\Drupal\Component\Render\MarkupInterface...
    *   Prefixes to add to the render variable. By default these will XSS admin
    *   filtered.
    *
    * @return array
+   *   A render array.
    */
   public static function prefix($thing) {
     $args = func_get_args();
@@ -34,20 +38,22 @@
       $output = static::makeRenderArray($output);
       $output['#prefix'] = $arg;
     }
+
     return $output;
   }
 
   /**
    * Suffixes a render variable.
    *
-   * @param string|\Drupal\Component\Utility\SafeStringInterface|array $thing
+   * @param string|\Drupal\Component\Render\MarkupInterface|array $thing
    *   A render variable. Either a string, an object that is safe or a render
    *   array.
-   * @param string|\Drupal\Component\Utility\SafeStringInterface...
+   * @param string|\Drupal\Component\Render\MarkupInterface...
    *   Suffixes to add to the render variable. By default these will XSS admin
    *   filtered.
    *
    * @return array
+   *   A render array.
    */
   public static function suffix($thing) {
     $args = func_get_args();
@@ -60,36 +66,38 @@
       $output = static::makeRenderArray($output);
       $output['#suffix'] = $arg;
     }
+
     return $output;
   }
 
   /**
    * Wraps a render variable.
    *
-   * @param string|\Drupal\Component\Utility\SafeStringInterface|array $thing
+   * @param string|\Drupal\Component\Render\MarkupInterface|array $thing
    *   A render variable. Either a string, an object that is safe or a render
    *   array.
-   * @param string|\Drupal\Component\Utility\SafeStringInterface $prefix
+   * @param string|\Drupal\Component\Render\MarkupInterface $prefix
    *   Prefix to add to the render variable. By default this will XSS admin
    *   filtered.
-   * @param string|\Drupal\Component\Utility\SafeStringInterface $suffix
+   * @param string|\Drupal\Component\Render\MarkupInterface $suffix
    *   Prefix to add to the render variable. By default this will XSS admin
    *   filtered.
    *
    * @return array
+   *   A render array.
    */
-
   public static function wrap($thing, $prefix, $suffix) {
     $output = static::makeRenderArray($thing);
     $output['#prefix'] = $prefix;
     $output['#suffix'] = $suffix;
+
     return $output;
   }
 
   /**
    * Converts a render variable into a render array.
    *
-   * @param string|\Drupal\Component\Utility\SafeStringInterface|array $thing
+   * @param string|\Drupal\Component\Render\MarkupInterface|array $thing
    *   A render variable. Either a string, an object that is safe or a render
    *   array.
    *
@@ -98,7 +106,7 @@
    */
   protected static function makeRenderArray($thing) {
     if (!is_array($thing)) {
-      if (SafeMarkup::isSafe($thing)) {
+      if ($thing instanceof MarkupInterface) {
         $output = [
           '#markup' => $thing,
         ];
@@ -117,4 +125,5 @@
+
     return $output;
   }
 
-}
\ No newline at end of file
+}