diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 5498bda..fd65f6b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3472,7 +3472,7 @@
 	 */
 	if (unused <= space_info->total_bytes) {
 		unused = space_info->total_bytes - unused;
-		if (unused >= num_bytes) {
+		if (unused >= orig_bytes) {
 			space_info->bytes_may_use += orig_bytes;
 			ret = 0;
 		} else {