diff --git a/fs/bcachefs/opts.c b/fs/bcachefs/opts.c
index e10fc1da71b1..1ccaed5c340b 100644
--- a/fs/bcachefs/opts.c
+++ b/fs/bcachefs/opts.c
@@ -482,6 +482,10 @@ int bch2_parse_one_mount_opt(struct bch_fs *c, struct bch_opts *opts,
 		val = "0";
 	}
 
+	/* Unknown options with invalid values are reported */
+	if (id < 0 && !val)
+		goto bad_val;
+
 	/* Unknown options are ignored: */
 	if (id < 0)
 		return 0;