Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 7162)
+++ wp-includes/formatting.php	(working copy)
@@ -1383,7 +1383,7 @@
  */
 function wp_html_excerpt( $str, $count ) {
 	$str = strip_tags( $str );
-	$str = html_entity_decode( $str, ENT_QUOTES);
+	$str = @html_entity_decode( $str, ENT_QUOTES, get_option('blog_charset') );
 	$str = mb_strcut( $str, 0, $count );
 	// remove part of an entity at the end
 	$str = preg_replace( '/&[^;\s]{0,6}$/', '', $str );