diff --git a/CHANGELOG.md b/CHANGELOG.md
index cbbeafe..35d0fea 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## To be Released
 
+* chore(go): use go 1.22
+* Raise default length from 20 to 64
+* Allow `_` only as special character
+
 ## 1.0.3
 
 * chore(go): use go 1.20
diff --git a/README.md b/README.md
index 936ed2f..2d63dc4 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 Simple password generator in Go. Use `crypto/rand`
 
 ```go
-// Passowrd of 20 characters
+// Password of 64 characters
 gopassword.Generate()
 
 // Password of 42 characters
diff --git a/go.mod b/go.mod
index d02acfe..a80f1a0 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/Scalingo/gopassword
 
-go 1.20
+go 1.22
 
 require github.com/stretchr/testify v1.9.0
 
diff --git a/gopassword.go b/gopassword.go
index 7a89347..43c679a 100644
--- a/gopassword.go
+++ b/gopassword.go
@@ -3,12 +3,14 @@ package gopassword
 import (
 	"crypto/rand"
 	"encoding/base64"
-	"fmt"
 	"strings"
 )
 
+const defaultLength = 64
+const defaultSpecialChar = "_"
+
 func Generate(n ...int) string {
-	length := 20
+	length := defaultLength
 	if len(n) > 0 {
 		length = n[0]
 	}
@@ -23,15 +25,8 @@ func Generate(n ...int) string {
 	randString := base64.StdEncoding.EncodeToString(randBytes)
 
 	password := randString[:length]
-	password = strings.Replace(password, "+", "_", -1)
-	password = strings.Replace(password, "/", "-", -1)
-
-	if password[0] == '-' {
-		password = fmt.Sprintf("_%s", password[1:])
-	}
-	if password[length-1] == '-' {
-		password = fmt.Sprintf("%s_", password[:length-1])
-	}
+	password = strings.ReplaceAll(password, "+", defaultSpecialChar)
+	password = strings.ReplaceAll(password, "/", defaultSpecialChar)
 
 	return password
 }
diff --git a/gopassword_test.go b/gopassword_test.go
index d846ba6..879204a 100644
--- a/gopassword_test.go
+++ b/gopassword_test.go
@@ -1,6 +1,7 @@
 package gopassword
 
 import (
+	"regexp"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -8,22 +9,34 @@ import (
 
 func TestGenerate(t *testing.T) {
 	t.Run("When we want to generate a password", func(t *testing.T) {
-		t.Run("By default, it should be 20 characters", func(t *testing.T) {
-			assert.Len(t, Generate(), 20)
+		t.Run("By default, it must be 64 characters", func(t *testing.T) {
+			assert.Len(t, Generate(), 64)
 		})
 
-		t.Run("With an argument, the generated password should have its length", func(t *testing.T) {
+		t.Run("With an argument, the generated password must have its length", func(t *testing.T) {
+			assert.Len(t, Generate(10), 10)
 			assert.Len(t, Generate(42), 42)
+			assert.Len(t, Generate(999), 999)
 		})
 
-		t.Run("With several arguments, only the first should be considered", func(t *testing.T) {
+		t.Run("With several arguments, only the first must be considered", func(t *testing.T) {
 			assert.Len(t, Generate(10, 20, 30), 10)
 		})
+
+		t.Run("It must contain only alphanumeric or underscore characters", func(t *testing.T) {
+			allowedCharacters := regexp.MustCompile("^[a-zA-Z0-9_]+$")
+
+			// Try various times to ensure the result is not casual
+			for range 1000 {
+				passwd := Generate(99)
+				assert.True(t, allowedCharacters.MatchString(passwd))
+			}
+		})
 	})
 
 	t.Run("Given a generated password", func(t *testing.T) {
 		passwd := Generate(20)
-		t.Run("The character frequency should be low", func(t *testing.T) {
+		t.Run("The character frequency must be low", func(t *testing.T) {
 			fm := frequencyMap(passwd)
 			maxFreq := max(fm)
 			assert.LessOrEqual(t, maxFreq, 3)