diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index d071bc4ae39ce53e147e236bd534cfc3f652c44e..109ff2420e0154d98dde3eabc51829fd59a07ff6 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -1374,6 +1374,9 @@ function format_string($string, array $args = array()) {
  * @see \Drupal\Component\Utility\String::checkPlain()
  * @see drupal_validate_utf8()
  * @ingroup sanitization
+ *
+ * @deprecated as of Drupal 8.0. Use
+ *   Drupal\Component\Utility\String::checkPlain() directly instead.
  */
 function check_plain($text) {
   return String::checkPlain($text);