diff --git a/go.mod b/go.mod
index 091239a..69e92c4 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/fumiama/fumitok
 
-go 1.22.1
+go 1.20
 
 require golang.org/x/crypto v0.28.0
 
diff --git a/token.go b/token.go
index 8cd26a9..e32c5d8 100644
--- a/token.go
+++ b/token.go
@@ -8,7 +8,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"hash/crc64"
-	"math/rand/v2"
+	"math/rand"
 	"time"
 
 	"golang.org/x/crypto/chacha20poly1305"