diff --git a/src/inventory/CallbackInventoryListener.php b/src/inventory/CallbackInventoryListener.php
index 8d08c4c78..98bf9a37d 100644
--- a/src/inventory/CallbackInventoryListener.php
+++ b/src/inventory/CallbackInventoryListener.php
@@ -30,31 +30,20 @@ class CallbackInventoryListener implements InventoryListener{
 
 	//TODO: turn the closure signatures into type aliases when PHPStan supports them
 
-	/**
-	 * @var \Closure|null
-	 * @phpstan-var (\Closure(Inventory, int, Item) : void)|null
-	 */
-	private $onSlotChangeCallback;
-	/**
-	 * @var \Closure|null
-	 * @phpstan-var (\Closure(Inventory, Item[]) : void)|null
-	 */
-	private $onContentChangeCallback;
-
 	/**
 	 * @phpstan-param (\Closure(Inventory, int, Item) : void)|null $onSlotChange
 	 * @phpstan-param (\Closure(Inventory, Item[]) : void)|null $onContentChange
 	 */
-	public function __construct(?\Closure $onSlotChange, ?\Closure $onContentChange){
+	public function __construct(
+		private ?\Closure $onSlotChange,
+		private ?\Closure $onContentChange
+	){
 		if($onSlotChange !== null){
 			Utils::validateCallableSignature(function(Inventory $inventory, int $slot, Item $oldItem) : void{}, $onSlotChange);
 		}
 		if($onContentChange !== null){
 			Utils::validateCallableSignature(function(Inventory $inventory, array $oldContents) : void{}, $onContentChange);
 		}
-
-		$this->onSlotChangeCallback = $onSlotChange;
-		$this->onContentChangeCallback = $onContentChange;
 	}
 
 	/**
@@ -72,8 +61,8 @@ class CallbackInventoryListener implements InventoryListener{
 	}
 
 	public function onSlotChange(Inventory $inventory, int $slot, Item $oldItem) : void{
-		if($this->onSlotChangeCallback !== null){
-			($this->onSlotChangeCallback)($inventory, $slot, $oldItem);
+		if($this->onSlotChange !== null){
+			($this->onSlotChange)($inventory, $slot, $oldItem);
 		}
 	}
 
@@ -81,8 +70,8 @@ class CallbackInventoryListener implements InventoryListener{
 	 * @param Item[] $oldContents
 	 */
 	public function onContentChange(Inventory $inventory, array $oldContents) : void{
-		if($this->onContentChangeCallback !== null){
-			($this->onContentChangeCallback)($inventory, $oldContents);
+		if($this->onContentChange !== null){
+			($this->onContentChange)($inventory, $oldContents);
 		}
 	}
 }
diff --git a/src/inventory/CreativeInventory.php b/src/inventory/CreativeInventory.php
index e71966f44..610f02392 100644
--- a/src/inventory/CreativeInventory.php
+++ b/src/inventory/CreativeInventory.php
@@ -34,7 +34,7 @@ final class CreativeInventory{
 	use SingletonTrait;
 
 	/** @var Item[] */
-	private $creative = [];
+	private array $creative = [];
 
 	private function __construct(){
 		$creativeItems = json_decode(file_get_contents(Path::join(\pocketmine\BEDROCK_DATA_PATH, "creativeitems.json")), true);
diff --git a/src/inventory/PlayerOffHandInventory.php b/src/inventory/PlayerOffHandInventory.php
index 1db8d63e0..bbcfd37d7 100644
--- a/src/inventory/PlayerOffHandInventory.php
+++ b/src/inventory/PlayerOffHandInventory.php
@@ -26,8 +26,7 @@ namespace pocketmine\inventory;
 use pocketmine\entity\Human;
 
 final class PlayerOffHandInventory extends SimpleInventory{
-	/** @var Human */
-	private $holder;
+	private Human $holder;
 
 	public function __construct(Human $player){
 		$this->holder = $player;