diff --git a/phpseclib/File/X509.php b/phpseclib/File/X509.php
index 73e7a113..af596807 100644
--- a/phpseclib/File/X509.php
+++ b/phpseclib/File/X509.php
@@ -2509,7 +2509,8 @@ class File_X509
                 $asn1->loadFilters($filters);
                 $result = '';
                 foreach ($dn['rdnSequence'] as $rdn) {
-                    foreach ($rdn as &$attr) {
+                    foreach ($rdn as $i=>$attr) {
+                        $attr = &$rdn[$i];
                         if (is_array($attr['value'])) {
                             foreach ($attr['value'] as $type => $v) {
                                 $type = array_search($type, $asn1->ANYmap, true);