diff --git a/CHANGELOG.md b/CHANGELOG.md
index e0a9874..9282be0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,8 @@ Record of the modification in project development.
 ## [Unreleased] - yyyy-mm-dd
 ### Added
 ### Changed
+- [Issue 26 : Update AN01 for btrfs](https://github.com/suikan4github/kaiten-yaki/issues/26)
+
 ### Deprecated
 ### Removed
 ### Fixed
diff --git a/appnote/an01_howtorecover.md b/appnote/an01_howtorecover.md
index 6cc3b9a..563fbc0 100644
--- a/appnote/an01_howtorecover.md
+++ b/appnote/an01_howtorecover.md
@@ -45,6 +45,11 @@ Following is the example. The (lvm/vg1-mate) is dependent on the system. It has
 ls
 set prefix=(lvm/vg1-mate)/boot/grub
 ```
+Note that above example assume the root volume format is usual one ( ex: ext4, jfs, xfs ). If the root volume is formatted by btrfs, above prefix doesn't work, it should contain the sub-volume name in the path :
+```
+ls
+set prefix=(lvm/vg1-mate)/@/boot/grub
+```
 
 Then, the third step is the same with the BIOS systems.