diff --git a/util/util_unsafe.go b/util/util_unsafe_go120.go
similarity index 87%
rename from util/util_unsafe.go
rename to util/util_unsafe_go120.go
index 840007a..d6be534 100644
--- a/util/util_unsafe.go
+++ b/util/util_unsafe_go120.go
@@ -1,5 +1,5 @@
-//go:build !appengine && !js
-// +build !appengine,!js
+//go:build !appengine && !js && !go1.21
+// +build !appengine,!js,!go1.21
 
 package util
 
diff --git a/util/util_unsafe_go121.go b/util/util_unsafe_go121.go
new file mode 100644
index 0000000..50c7fce
--- /dev/null
+++ b/util/util_unsafe_go121.go
@@ -0,0 +1,18 @@
+//go:build !appengine && !js && go1.21
+// +build !appengine,!js,go1.21
+
+package util
+
+import (
+	"unsafe"
+)
+
+// BytesToReadOnlyString returns a string converted from given bytes.
+func BytesToReadOnlyString(b []byte) string {
+	return unsafe.String(unsafe.SliceData(b), len(b))
+}
+
+// StringToReadOnlyBytes returns bytes converted from given string.
+func StringToReadOnlyBytes(s string) []byte {
+	return unsafe.Slice(unsafe.StringData(s), len(s))
+}