diff --git a/comment_notify.module b/comment_notify.module
index 506f4a9..bf978da 100644
--- a/comment_notify.module
+++ b/comment_notify.module
@@ -249,13 +249,23 @@ function comment_notify_comment_update($comment) {
 
 function comment_notify_comment_insert($comment) {
   module_load_include('inc', 'comment_notify', 'comment_notify');
-
   global $user;
   // For new comments, we first build up a string to be used as the identifier for the alert.
   // This identifier is used to later unsubscribe the user or allow them to
   // potentially edit their comment / preferences if they are anonymous.
   // The string is built from their mail and comment identifier.
-  $mail = empty($comment->mail) ? $user->mail : $comment->mail;
+  if (empty($comment->mail)) {
+    if (empty($user->mail)) {
+      // We're only using this to seed a hash which might get used later, so get a random value.
+      $mail = user_password();
+    }
+    else {
+      $mail = $user->mail;
+    }
+  }
+  else {
+    $mail = $comment->mail;
+  }
   $notify_hash = drupal_get_token($mail . $comment->cid);
 
   if (!empty($comment->notify)) {