--- modules/comment/comment.module.orig	2011-05-12 23:46:38.000000000 +1000
+++ modules/comment/comment.module	2011-05-12 23:49:36.000000000 +1000
@@ -2180,7 +2180,9 @@
     // 1) Filter it into HTML
     // 2) Strip out all HTML tags
     // 3) Convert entities back to plain-text.
-    $comment->subject = truncate_utf8(trim(decode_entities(strip_tags(check_markup($comment->comment_body[LANGUAGE_NONE][0]['value'], $comment->comment_body[LANGUAGE_NONE][0]['format'])))), 29, TRUE);
+    if (isset($comment->comment_body[LANGUAGE_NONE][0])) {
+      $comment->subject = truncate_utf8(trim(decode_entities(strip_tags(check_markup($comment->comment_body[LANGUAGE_NONE][0]['value'], $comment->comment_body[LANGUAGE_NONE][0]['format'])))), 29, TRUE);
+    }
     // Edge cases where the comment body is populated only by HTML tags will
     // require a default subject.
     if ($comment->subject == '') {