diff --git a/fs/bcachefs/bcachefs_format.h b/fs/bcachefs/bcachefs_format.h
index 1bebba881d89..d801e19cb489 100644
--- a/fs/bcachefs/bcachefs_format.h
+++ b/fs/bcachefs/bcachefs_format.h
@@ -1555,6 +1555,12 @@ enum btree_id {
 	BTREE_ID_NR
 };
 
+/*
+ * Maximum number of btrees that we will _ever_ have under the current scheme,
+ * where we refer to them with bitfields
+ */
+#define BTREE_ID_NR_MAX		64
+
 static inline bool btree_id_is_alloc(enum btree_id id)
 {
 	switch (id) {
diff --git a/fs/bcachefs/recovery.c b/fs/bcachefs/recovery.c
index 1266916ac03f..63f990f5c63a 100644
--- a/fs/bcachefs/recovery.c
+++ b/fs/bcachefs/recovery.c
@@ -35,6 +35,9 @@
 
 void bch2_btree_lost_data(struct bch_fs *c, enum btree_id btree)
 {
+	if (btree >= BTREE_ID_NR_MAX)
+		return;
+
 	u64 b = BIT_ULL(btree);
 
 	if (!(c->sb.btrees_lost_data & b)) {