diff --git a/sys/kern/subr_prf.c b/sys/kern/subr_prf.c
--- a/sys/kern/subr_prf.c
+++ b/sys/kern/subr_prf.c
@@ -1180,7 +1180,7 @@
 		 */
 		error = sysctl_handle_opaque(oidp,
 					     mbp->msg_ptr + rindex_modulo,
-					     n - rindex_modulo,
+					     n,
 					     req);
 	} else {
 		/*