diff --git a/exceptions/MDInvalidNodaLinkLocIdIsSh.php b/exceptions/MDInvalidNodaLinkLocIdIsSh.php
index 5459d5e..89e4447 100644
--- a/exceptions/MDInvalidNodaLinkLocIdIsSh.php
+++ b/exceptions/MDInvalidNodaLinkLocIdIsSh.php
@@ -6,7 +6,7 @@ declare(strict_types = 1);
  * headings (subject headings are a dedicated, full vocabulary according to
  * md's definition).
  */
-class MDInvalidNodaLinkLocIdIsSh extends MDInvalidNodaLinkException {
+final class MDInvalidNodaLinkLocIdIsSh extends MDInvalidNodaLinkException {
     /**
      * Error message.
      *