diff --git a/lib/libc/gen/getfsent.3 b/lib/libc/gen/getfsent.3
index bbf21512dcb4..b06e56763fc2 100644
--- a/lib/libc/gen/getfsent.3
+++ b/lib/libc/gen/getfsent.3
@@ -150,6 +150,13 @@ returns nothing.
 If the environment variable
 .Pa PATH_FSTAB
 is set all operations are performed against the specified file.
+.Pa PATH_FSTAB
+will not be honored if the process environment or memory address space is
+considred
+.Dq tainted .
+(See
+.Fn issetugid
+for more information.)
 .El
 .Sh FILES
 .Bl -tag -width /etc/fstab -compact
diff --git a/sbin/mount/mount.8 b/sbin/mount/mount.8
index 741904bdd4a4..d59154c8608b 100644
--- a/sbin/mount/mount.8
+++ b/sbin/mount/mount.8
@@ -417,6 +417,13 @@ support for a particular file system might be provided either on a static
 If the environment variable
 .Pa PATH_FSTAB
 is set all operations are performed against the specified file.
+.Pa PATH_FSTAB
+will not be honored if the process environment or memory address space is
+considred
+.Dq tainted .
+(See
+.Fn issetugid
+for more information.)
 .El
 .Sh FILES
 .Bl -tag -width /etc/fstab -compact
diff --git a/sbin/umount/umount.8 b/sbin/umount/umount.8
index bdaa34b5638d..007ce15c0bf6 100644
--- a/sbin/umount/umount.8
+++ b/sbin/umount/umount.8
@@ -126,6 +126,13 @@ is unmounted.
 If the environment variable
 .Pa PATH_FSTAB
 is set all operations are performed against the specified file.
+.Pa PATH_FSTAB
+will not be honored if the process environment or memory address space is
+considred
+.Dq tainted .
+(See
+.Fn issetugid
+for more information.)
 .El
 .Sh FILES
 .Bl -tag -width /etc/fstab -compact