Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 10506)
+++ wp-includes/formatting.php	(working copy)
@@ -2258,7 +2258,7 @@
  */
 function wp_html_excerpt( $str, $count ) {
 	$str = strip_tags( $str );
-	$str = mb_strcut( $str, 0, $count );
+	$str = mb_substr( $str, 0, $count );
 	// remove part of an entity at the end
 	$str = preg_replace( '/&[^;\s]{0,6}$/', '', $str );
 	return $str;