diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 5a7ddcff406b8..1b9ede123ffb7 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3443,7 +3443,8 @@ static int cache_save_setup(struct btrfs_block_group_cache *block_group,
 		/*
 		 * don't bother trying to write stuff out _if_
 		 * a) we're not cached,
-		 * b) we're with nospace_cache mount option.
+		 * b) we're with nospace_cache mount option,
+		 * c) we're with v2 space_cache (FREE_SPACE_TREE).
 		 */
 		dcs = BTRFS_DC_WRITTEN;
 		spin_unlock(&block_group->lock);