diff --git a/sys/kern/kern_prot.c b/sys/kern/kern_prot.c
--- a/sys/kern/kern_prot.c
+++ b/sys/kern/kern_prot.c
@@ -2921,7 +2921,8 @@
  * Normalizes a set of groups to be applied to a 'struct ucred'.
  *
  * Normalization ensures that the supplementary groups are sorted in ascending
- * order and do not contain duplicates.
+ * order and do not contain duplicates.  This allows group_is_supplementary
+ * to do a binary search.
  */
 static void
 groups_normalize(int *ngrp, gid_t *groups)