diff --git a/src/FontLib/BinaryStream.php b/src/FontLib/BinaryStream.php
index 2b6b7eb..c93b83c 100644
--- a/src/FontLib/BinaryStream.php
+++ b/src/FontLib/BinaryStream.php
@@ -411,7 +411,9 @@ public function w($type, $data) {
 
           $ret = 0;
           for ($i = 0; $i < $type[1]; $i++) {
-            $ret += $this->w($type[0], $data[$i]);
+            if (isset($data[$i])) {
+              $ret += $this->w($type[0], $data[$i]);
+            }
           }
 
           return $ret;