diff --git a/fs/btrfs/free-space-cache.h b/fs/btrfs/free-space-cache.h
index f251865..33178c4 100644
--- a/fs/btrfs/free-space-cache.h
+++ b/fs/btrfs/free-space-cache.h
@@ -37,7 +37,7 @@
 	int total_bitmaps;
 	int unit;
 	u64 start;
-	struct btrfs_free_space_op *op;
+	const struct btrfs_free_space_op *op;
 	void *private;
 	struct mutex cache_writeout_mutex;
 	struct list_head trimming_ranges;