--- sys/fs/nfsclient/nfs_clvfsops.c	2020-10-24 10:59:27.299934000 -0700
+++ sys/fs/nfsclient/nfs_clvfsops.c	2020-10-24 11:14:10.875430000 -0700
@@ -1010,7 +1010,7 @@ nfs_mount(struct mount *mp)
 			goto out;
 		}
 		ret = sscanf(opt, "%d", &args.readahead);
-		if (ret != 1 || args.readahead <= 0) {
+		if (ret != 1 || args.readahead < 0) {
 			vfs_mount_error(mp, "illegal readahead: %s",
 			    opt);
 			error = EINVAL;