diff --git a/lib/phpmailer/class.smtp.php b/lib/phpmailer/class.smtp.php
index a4013745566..3b0b0b59a25 100644
--- a/lib/phpmailer/class.smtp.php
+++ b/lib/phpmailer/class.smtp.php
@@ -332,6 +332,13 @@ class SMTP
             # smaller lines
             while(strlen($line) > $max_line_length) {
                 $pos = strrpos(substr($line,0,$max_line_length)," ");
+
+                // Fix from http://www.addict3d.org/index.php?page=viewarticle&type=security&ID=4079
+                if (!$pos) {
+                    $pos = $max_line_length - 1;
+                }
+                // End of fix
+
                 $lines_out[] = substr($line,0,$pos);
                 $line = substr($line,$pos + 1);
                 # if we are processing headers we need to