diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index 444c2bef2608..b02d65b384f8 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -1170,6 +1170,7 @@ brelse(struct buf *bp)
 
 	if (bp->b_iocmd == BIO_WRITE &&
 	    (bp->b_ioflags & BIO_ERROR) &&
+	    bp->b_error != ENXIO &&
 	    !(bp->b_flags & B_INVAL)) {
 		/*
 		 * Failed write, redirty.  Must clear BIO_ERROR to prevent
@@ -1177,6 +1178,9 @@ brelse(struct buf *bp)
 		 * this case is not run and the next case is run to 
 		 * destroy the buffer.  B_INVAL can occur if the buffer
 		 * is outside the range supported by the underlying device.
+		 * If the error is that the device went away (ENXIO), we
+		 * shouldn't redirty the buffer either, but discard the
+		 * data too.
 		 */
 		bp->b_ioflags &= ~BIO_ERROR;
 		bdirty(bp);
diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
index dfb46e29c8a9..6a615b1e795c 100644
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -1286,8 +1286,13 @@ dounmount(mp, flags, td)
 		error = VFS_UNMOUNT(mp, flags, td);
 	}
 	vn_finished_write(mp);
-	if (error) {
-		/* Undo cdir/rdir and rootvnode changes made above. */
+	/*
+	 * If we failed to flush the dirty blocks for this mount point,
+	 * undo all the cdir/rdir and rootvnode changes we made above.
+	 * Unless we failed to do so because the device is reporting that
+	 * it doesn't exist anymore.
+	 */
+	if (error && error != ENXIO) {
 		if ((flags & MNT_FORCE) &&
 		    VFS_ROOT(mp, LK_EXCLUSIVE, &fsrootvp, td) == 0) {
 			if (mp->mnt_vnodecovered != NULL)