diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index bc09131adb8..56f9d604b9e 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -320,7 +320,8 @@ SYSCTL_COUNTER_U64(_vfs, OID_AUTO, notbufdflushes, CTLFLAG_RD, &notbufdflushes,
 static long barrierwrites;
 SYSCTL_LONG(_vfs, OID_AUTO, barrierwrites, CTLFLAG_RW | CTLFLAG_STATS,
     &barrierwrites, 0, "Number of barrier writes");
-SYSCTL_INT(_vfs, OID_AUTO, unmapped_buf_allowed, CTLFLAG_RD,
+SYSCTL_INT(_vfs, OID_AUTO, unmapped_buf_allowed,
+    CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
     &unmapped_buf_allowed, 0,
     "Permit the use of the unmapped i/o");
 int maxbcachebuf = MAXBCACHEBUF;