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
@@ -2041,8 +2041,7 @@
 	mac_cred_init(cr);
 #endif
 	cr->cr_groups = cr->cr_smallgroups;
-	cr->cr_agroups =
-	    sizeof(cr->cr_smallgroups) / sizeof(cr->cr_smallgroups[0]);
+	cr->cr_agroups = nitems(cr->cr_smallgroups);
 	return (cr);
 }