diff --git a/src/Utils/BaseSet.php b/src/Utils/BaseSet.php
index 25069f2..0640fe7 100644
--- a/src/Utils/BaseSet.php
+++ b/src/Utils/BaseSet.php
@@ -12,7 +12,7 @@ abstract class BaseSet implements \Iterator, \ArrayAccess, \Countable
 
     protected array $array = [];
 
-    public function merge(self $objectSet, bool $allowReplace = false) : self
+    public function merge(self $objectSet, bool $allowReplace = false) : static
     {
         if (!$objectSet instanceof static) {
             throw new \Exception('I can only merge Sets of same type');
@@ -83,7 +83,7 @@ public function offsetUnset($offset) : void
         unset($this->array[$offset]);
     }
 
-    abstract protected function mergeImpl(self $objectSet, bool $allowReplace) : self;
+    abstract protected function mergeImpl(self $objectSet, bool $allowReplace) : static;
 
     abstract protected function offsetSetImpl($offset, object $object) : void;
 }
diff --git a/src/Utils/Json.php b/src/Utils/Json.php
index 68cecf1..4c8fc3a 100644
--- a/src/Utils/Json.php
+++ b/src/Utils/Json.php
@@ -15,7 +15,7 @@ private function __construct(?string $json, ?\Infinityloop\Utils\Json\JsonContra
         $this->inner = $data;
     }
 
-    public static function fromString(string $json) : self
+    public static function fromString(string $json) : static
     {
         return new self($json, null);
     }
diff --git a/src/Utils/Json/JsonContract.php b/src/Utils/Json/JsonContract.php
index cde2880..113e4b6 100644
--- a/src/Utils/Json/JsonContract.php
+++ b/src/Utils/Json/JsonContract.php
@@ -14,7 +14,7 @@ abstract class JsonContract implements \Countable, \IteratorAggregate, \ArrayAcc
         \JSON_UNESCAPED_SLASHES |
         \JSON_PRESERVE_ZERO_FRACTION;
 
-    abstract public static function fromString(string $json) : self;
+    abstract public static function fromString(string $json) : static;
 
     abstract public function toString() : string;
 
diff --git a/src/Utils/Json/MapJson.php b/src/Utils/Json/MapJson.php
index 03e7eeb..c8c7d27 100644
--- a/src/Utils/Json/MapJson.php
+++ b/src/Utils/Json/MapJson.php
@@ -15,7 +15,7 @@ private function __construct(?string $json, ?\stdClass $data)
         $this->data = $data;
     }
 
-    public static function fromString(string $json) : self
+    public static function fromString(string $json) : static
     {
         return new self($json, null);
     }
diff --git a/src/Utils/Json/SequentialJson.php b/src/Utils/Json/SequentialJson.php
index 612df5a..ec317b7 100644
--- a/src/Utils/Json/SequentialJson.php
+++ b/src/Utils/Json/SequentialJson.php
@@ -19,7 +19,7 @@ private function __construct(?string $json, ?array $data)
         $this->data = $data;
     }
 
-    public static function fromString(string $json) : self
+    public static function fromString(string $json) : static
     {
         return new self($json, null);
     }
diff --git a/src/Utils/ObjectMap.php b/src/Utils/ObjectMap.php
index 675cf93..908c4a0 100644
--- a/src/Utils/ObjectMap.php
+++ b/src/Utils/ObjectMap.php
@@ -18,7 +18,7 @@ public function key() : string
         return \key($this->array);
     }
 
-    protected function mergeImpl(BaseSet $objectSet, bool $allowReplace = false) : self
+    protected function mergeImpl(BaseSet $objectSet, bool $allowReplace = false) : static
     {
         foreach ($objectSet as $offset => $object) {
             if (!$allowReplace && $this->offsetExists($offset)) {
diff --git a/src/Utils/ObjectSet.php b/src/Utils/ObjectSet.php
index 64b0598..fb5b6fb 100644
--- a/src/Utils/ObjectSet.php
+++ b/src/Utils/ObjectSet.php
@@ -18,7 +18,7 @@ public function key() : int
         return \key($this->array);
     }
 
-    protected function mergeImpl(BaseSet $objectSet, bool $allowReplace = false) : self
+    protected function mergeImpl(BaseSet $objectSet, bool $allowReplace = false) : static
     {
         foreach ($objectSet as $offset => $object) {
             $this->offsetSet($allowReplace