diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index 47a01da..9efcab0 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -1556,13 +1556,15 @@ function format_string($string, array $args = array()) {
  *   The text to be checked or processed.
  *
  * @return
- *   An HTML safe version of $text, or an empty string if $text is not
- *   valid UTF-8.
+ *   An HTML safe version of $text, or FALSE if $text is not valid UTF-8.
  *
  * @see drupal_validate_utf8()
  * @ingroup sanitization
  */
 function check_plain($text) {
+  if (!drupal_validate_utf8($text)) {
+    return FALSE;
+  }
   return htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
 }