diff --git a/Documentation/btrfs-mount.txt b/Documentation/btrfs-mount.txt
index 53f88c98..4fb71377 100644
--- a/Documentation/btrfs-mount.txt
+++ b/Documentation/btrfs-mount.txt
@@ -200,6 +200,8 @@ attributes the `chattr`(1) utility
 
 *S* -- synchronous updates
 
+*X* -- no compression
+
 For descriptions of these attribute flags, please refer to the
 `chattr`(1) man page.