diff --git a/src/File.php b/src/File.php
index d0bb9ec2..40aad929 100644
--- a/src/File.php
+++ b/src/File.php
@@ -15,10 +15,10 @@
 
 final class File
 {
-    private $name;
-    private $template;
-    private $period;
-    private $holder;
+    private string $name;
+    private Template $template;
+    private Period $period;
+    private Holder $holder;
 
     private function __construct(
         string $name,
diff --git a/src/Header.php b/src/Header.php
index f12b6884..a048e797 100644
--- a/src/Header.php
+++ b/src/Header.php
@@ -15,11 +15,11 @@
 
 final class Header
 {
-    private $template;
-    private $period;
-    private $holder;
-    private $file;
-    private $url;
+    private Template $template;
+    private Period $period;
+    private Holder $holder;
+    private File $file;
+    private Url $url;
 
     private function __construct(
         Template $template,
diff --git a/src/Holder.php b/src/Holder.php
index 01e3fc13..65b8f70d 100644
--- a/src/Holder.php
+++ b/src/Holder.php
@@ -17,7 +17,7 @@
 
 final class Holder
 {
-    private $value;
+    private string $value;
 
     private function __construct(string $value)
     {
diff --git a/src/Range.php b/src/Range.php
index fd94ebbf..93ed200c 100644
--- a/src/Range.php
+++ b/src/Range.php
@@ -15,7 +15,7 @@
 
 final class Range implements Period
 {
-    private $value;
+    private string $value;
 
     private function __construct(string $value)
     {
diff --git a/src/Template.php b/src/Template.php
index 1f64f33a..8d2c7937 100644
--- a/src/Template.php
+++ b/src/Template.php
@@ -15,7 +15,7 @@
 
 final class Template
 {
-    private $value;
+    private string $value;
 
     private function __construct(string $value)
     {
diff --git a/src/Type/MIT.php b/src/Type/MIT.php
index 685b884e..50d746ac 100644
--- a/src/Type/MIT.php
+++ b/src/Type/MIT.php
@@ -22,15 +22,8 @@
 
 final class MIT
 {
-    /**
-     * @var File
-     */
-    private $file;
-
-    /**
-     * @var Header
-     */
-    private $header;
+    private File $file;
+    private Header $header;
 
     private function __construct(
         string $name,
diff --git a/src/Url.php b/src/Url.php
index 19310ebe..506bed35 100644
--- a/src/Url.php
+++ b/src/Url.php
@@ -15,7 +15,7 @@
 
 final class Url
 {
-    private $value;
+    private string $value;
 
     private function __construct(string $value)
     {
diff --git a/src/Year.php b/src/Year.php
index a83d0a5f..a223a6a5 100644
--- a/src/Year.php
+++ b/src/Year.php
@@ -15,7 +15,7 @@
 
 final class Year implements Period
 {
-    private $value;
+    private string $value;
 
     private function __construct(string $value)
     {