diff --git a/composer.json b/composer.json
index fae3834..d0cc8fb 100644
--- a/composer.json
+++ b/composer.json
@@ -18,7 +18,7 @@
 		}
 	],
 	"require": {
-		"php": ">=7.1"
+		"php": ">=7.4"
 	},
 	"autoload": {
 		"psr-4": {
diff --git a/src/IdentityCard.php b/src/IdentityCard.php
index 4f5df48..8f7b67a 100644
--- a/src/IdentityCard.php
+++ b/src/IdentityCard.php
@@ -9,21 +9,21 @@ class IdentityCard
 	 *
 	 * @var  IdentityCard|null
 	 */
-	protected static $instance;
+	protected static ?IdentityCard $instance = null;
 
 	/**
 	 * The user id card.
 	 *
 	 * @var  string
 	 */
-	protected static $idCard;
+	protected static string $idCard;
 
 	/**
 	 * Get the lcoale slog.
 	 *
 	 * @var  string
 	 */
-	protected static $locale;
+	protected static string $locale;
 
 	/**
 	 * Create an new IdentityCard instance.