diff --git a/composer.json b/composer.json
index b5784b8..48a1999 100644
--- a/composer.json
+++ b/composer.json
@@ -2,7 +2,7 @@
     "name": "printnode/printnode-php",
     "description": "Connect any printer to your application with PrintNode Client and easy to use JSON API",
     "require": {
-        "php": ">=5.3.2",
+        "php": ">=8.1",
         "ext-curl": "*"
     },
     "keywords": [
diff --git a/src/PrintNode/Entity.php b/src/PrintNode/Entity.php
index 1a71c51..2430020 100755
--- a/src/PrintNode/Entity.php
+++ b/src/PrintNode/Entity.php
@@ -102,7 +102,7 @@ public function mapValuesFromJson($json)
      * 
      * @return string
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
         
         $json = array();
@@ -132,4 +132,4 @@ public function __toString() {
         
     }
     
-}
\ No newline at end of file
+}
diff --git a/src/PrintNode/EntityDynamic.php b/src/PrintNode/EntityDynamic.php
index af474eb..3ff6c41 100644
--- a/src/PrintNode/EntityDynamic.php
+++ b/src/PrintNode/EntityDynamic.php
@@ -4,7 +4,7 @@
 
 abstract class EntityDynamic extends Entity
 {
-    
+
     /**
      * Reference to the client
      * @var Client
@@ -12,7 +12,7 @@ abstract class EntityDynamic extends Entity
     protected static $protectedProperties = array(
         'client',
     );
-    
+
     /**
      * Set property on entity
      * @param mixed $propertyName
@@ -21,58 +21,58 @@ abstract class EntityDynamic extends Entity
      */
     public function __set($propertyName, $value)
     {
-        
+
         if (\in_array($propertyName, self::$protectedProperties)) {
             throw new \PrintNode\Exception\InvalidArgumentException($propertyName . ' is a protected property.');
         }
-        
+
         $this->$propertyName = $value;
-        
+
     }
-    
+
     /**
      * Maps a json object to this entity
-     * 
+     *
      * @param string $json The JSON to map to this entity
      * @return string
      */
     public function mapValuesFromJson($json)
     {
-        
+
         foreach ($json as $key => $value) {
             $this->$key = $value;
         }
-        
+
         return true;
-        
+
     }
-    
+
     /**
      * Implements the jsonSerialize method
-     * 
+     *
      * @return string
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
-        
+
         $refClass = new \ReflectionClass($this);
-        
+
         $properties = get_object_vars($this);
-        
+
         $json = array();
-        
+
         foreach ($properties as $property => $value) {
-            
+
             if (in_array($property, self::$protectedProperties)) {
                 continue;
             }
-            
+
             $json[$property] = $value;
-            
+
         }
-        
+
         return $json;
-        
+
     }
-    
-}
\ No newline at end of file
+
+}