diff --git a/src/nusoap.php b/src/nusoap.php
index ddd7029..f5bf034 100644
--- a/src/nusoap.php
+++ b/src/nusoap.php
@@ -6843,7 +6843,7 @@ function __construct($xml, $encoding = 'UTF-8', $method = '', $decode_utf8 = tru
                 $substrXml = $xml;
                 foreach($this->attachments as $key => $attachment) {
                     $startPos = max(
-                        stripos($substrXml, $attachment['boundaryStr']),
+                        isset($attachment['boundaryStr']) ? stripos($substrXml, $attachment['boundaryStr']) : false,
                         (array_key_exists('Content-Type', $attachment) ? stripos($substrXml, $attachment['Content-Type']) : 0),
                         (array_key_exists('Content-Id', $attachment) ? stripos($substrXml, $attachment['Content-Id']) : 0),
                         (array_key_exists('Content-Transfer-Encoding', $attachment) ? stripos($substrXml, $attachment['Content-Transfer-Encoding']) : 0)