diff --git a/algo/qmc/key_mmkv.go b/algo/qmc/key_mmkv.go
index 742b4e2..3dff9eb 100644
--- a/algo/qmc/key_mmkv.go
+++ b/algo/qmc/key_mmkv.go
@@ -117,6 +117,9 @@ func getDefaultMMKVDir() (string, error) {
 	return mmkvDir, nil
 }
 
+// normalizeUnicode normalizes unicode string to NFC.
+// since macOS may change some characters in the file name.
+// e.g. "ぜ"(e3 81 9c) -> "ぜ"(e3 81 9b e3 82 99)
 func normalizeUnicode(str string) string {
 	return norm.NFC.String(str)
 }