diff --git a/wp-admin/includes/file.php b/wp-admin/includes/file.php
index ca424264bc..8f88de48e9 100644
--- a/wp-admin/includes/file.php
+++ b/wp-admin/includes/file.php
@@ -667,7 +667,7 @@ function _unzip_file_pclzip($file, $to, $needed_dirs = array()) {
 	global $wp_filesystem;
 
 	// See #15789 - PclZip uses string functions on binary data, If it's overloaded with Multibyte safe functions the results are incorrect.
-	if ( ini_get('mbstring.func_overload') && function_exists('mb_internal_encoding') ) {
+	if ( ( ini_get('mbstring.func_overload') & 2 ) && function_exists('mb_internal_encoding') ) {
 		$previous_encoding = mb_internal_encoding();
 		mb_internal_encoding('ISO-8859-1');
 	}