diff --git a/wp-admin/includes/file.php b/wp-admin/includes/file.php
index 68a77b292e..c2464f26b8 100644
--- a/wp-admin/includes/file.php
+++ b/wp-admin/includes/file.php
@@ -652,12 +652,23 @@ function _unzip_file_ziparchive($file, $to, $needed_dirs = array() ) {
 function _unzip_file_pclzip($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') ) {
+		$previous_encoding = mb_internal_encoding();
+		mb_internal_encoding('ISO-8859-1');
+	}
+
 	require_once(ABSPATH . 'wp-admin/includes/class-pclzip.php');
 
 	$archive = new PclZip($file);
 
+	$archive_files = $archive->extract(PCLZIP_OPT_EXTRACT_AS_STRING);
+
+	if ( isset($previous_encoding) )
+		mb_internal_encoding($previous_encoding);
+
 	// Is the archive valid?
-	if ( false == ($archive_files = $archive->extract(PCLZIP_OPT_EXTRACT_AS_STRING)) )
+	if ( false === $archive_files )
 		return new WP_Error('incompatible_archive', __('Incompatible Archive.'), $archive->errorInfo(true));
 
 	if ( 0 == count($archive_files) )