diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 444e9c89ff3e9a..b67c965725ea69 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -2547,6 +2547,19 @@ int btrfs_inc_block_group_ro(struct btrfs_block_group *cache,
 	int ret;
 	bool dirty_bg_running;
 
+	/*
+	 * This can only happen when we are doing read-only scrub on read-only
+	 * mount.
+	 * In that case we should not start a new transaction on read-only fs.
+	 * Thus here we skip all chunk allocations.
+	 */
+	if (sb_rdonly(fs_info->sb)) {
+		mutex_lock(&fs_info->ro_block_group_mutex);
+		ret = inc_block_group_ro(cache, 0);
+		mutex_unlock(&fs_info->ro_block_group_mutex);
+		return ret;
+	}
+
 	do {
 		trans = btrfs_join_transaction(fs_info->extent_root);
 		if (IS_ERR(trans))