diff --git a/unmaintained/fix_dat/fix_dat.go b/unmaintained/fix_dat/fix_dat.go
index 486da4a78..85ab15f6a 100644
--- a/unmaintained/fix_dat/fix_dat.go
+++ b/unmaintained/fix_dat/fix_dat.go
@@ -21,6 +21,9 @@ var (
 
 /*
 This is to resolve an one-time issue that caused inconsistency with .dat and .idx files.
+In this case, the .dat file contains all data, but some of deletion caused incorrect offset.
+The .idx has all correct offsets.
+
 1. fix the .dat file, a new .dat_fixed file will be generated.
 	go run fix_dat.go -volumeId=9 -dir=/Users/chrislu/Downloads
 2. move the original .dat and .idx files to some backup folder, and rename .dat_fixed to .dat file