diff --git a/src/network/mcpe/convert/TypeConverter.php b/src/network/mcpe/convert/TypeConverter.php
index b421fc8c9..088f202fd 100644
--- a/src/network/mcpe/convert/TypeConverter.php
+++ b/src/network/mcpe/convert/TypeConverter.php
@@ -38,11 +38,13 @@ use pocketmine\network\mcpe\protocol\types\GameMode as ProtocolGameMode;
 use pocketmine\network\mcpe\protocol\types\inventory\ContainerIds;
 use pocketmine\network\mcpe\protocol\types\inventory\ItemStack;
 use pocketmine\network\mcpe\protocol\types\inventory\NetworkInventoryAction;
+use pocketmine\network\mcpe\protocol\types\inventory\UIInventorySlotOffset;
 use pocketmine\network\mcpe\protocol\types\recipe\RecipeIngredient;
 use pocketmine\player\GameMode;
 use pocketmine\player\Player;
 use pocketmine\utils\AssumptionFailedError;
 use pocketmine\utils\SingletonTrait;
+use function array_key_exists;
 
 class TypeConverter{
 	use SingletonTrait;
@@ -168,21 +170,21 @@ class TypeConverter{
 		switch($action->sourceType){
 			case NetworkInventoryAction::SOURCE_CONTAINER:
 				if($action->windowId === ContainerIds::UI and $action->inventorySlot > 0){
-					if($action->inventorySlot === 50){
+					if($action->inventorySlot === UIInventorySlotOffset::CREATED_ITEM_OUTPUT){
 						return null; //useless noise
 					}
-					if($action->inventorySlot >= 28 and $action->inventorySlot <= 31){
+					if(array_key_exists($action->inventorySlot, UIInventorySlotOffset::CRAFTING2X2_INPUT)){
 						$window = $player->getCraftingGrid();
 						if($window->getGridWidth() !== CraftingGrid::SIZE_SMALL){
 							throw new \UnexpectedValueException("Expected small crafting grid");
 						}
-						$slot = $action->inventorySlot - 28;
-					}elseif($action->inventorySlot >= 32 and $action->inventorySlot <= 40){
+						$slot = UIInventorySlotOffset::CRAFTING2X2_INPUT[$action->inventorySlot];
+					}elseif(array_key_exists($action->inventorySlot, UIInventorySlotOffset::CRAFTING3X3_INPUT)){
 						$window = $player->getCraftingGrid();
 						if($window->getGridWidth() !== CraftingGrid::SIZE_BIG){
 							throw new \UnexpectedValueException("Expected big crafting grid");
 						}
-						$slot = $action->inventorySlot - 32;
+						$slot = UIInventorySlotOffset::CRAFTING3X3_INPUT[$action->inventorySlot];
 					}else{
 						throw new \UnexpectedValueException("Unhandled magic UI slot offset $action->inventorySlot");
 					}
@@ -225,4 +227,4 @@ class TypeConverter{
 				throw new \UnexpectedValueException("Unknown inventory source type $action->sourceType");
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/src/network/mcpe/protocol/types/inventory/UIInventorySlotOffset.php b/src/network/mcpe/protocol/types/inventory/UIInventorySlotOffset.php
new file mode 100644
index 000000000..12e2c60eb
--- /dev/null
+++ b/src/network/mcpe/protocol/types/inventory/UIInventorySlotOffset.php
@@ -0,0 +1,105 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+*/
+
+declare(strict_types=1);
+
+namespace pocketmine\network\mcpe\protocol\types\inventory;
+
+final class UIInventorySlotOffset{
+
+	private function __construct(){
+		//NOOP
+	}
+
+	public const CURSOR = 0;
+	public const ANVIL = [
+		1 => 0,
+		2 => 1,
+	];
+	public const STONE_CUTTER_INPUT = 3;
+	public const TRADE2_INGREDIENT = [
+		4 => 0,
+		5 => 1,
+	];
+	public const TRADE_INGREDIENT = [
+		6 => 0,
+		7 => 1,
+	];
+	public const MATERIAL_REDUCER_INPUT = 8;
+	public const LOOM = [
+		9 => 0,
+		10 => 1,
+		11 => 2,
+	];
+	public const CARTOGRAPHY_TABLE = [
+		12 => 0,
+		13 => 1,
+	];
+	public const ENCHANTING_TABLE = [
+		14 => 0,
+		15 => 1,
+	];
+	public const GRINDSTONE = [
+		16 => 0,
+		17 => 1,
+	];
+	public const COMPOUND_CREATOR_INPUT = [
+		18 => 0,
+		19 => 1,
+		20 => 2,
+		21 => 3,
+		22 => 4,
+		23 => 5,
+		24 => 6,
+		25 => 7,
+		26 => 8,
+	];
+	public const BEACON_PAYMENT = 27;
+	public const CRAFTING2X2_INPUT = [
+		28 => 0,
+		29 => 1,
+		30 => 2,
+		31 => 3,
+	];
+	public const CRAFTING3X3_INPUT = [
+		32 => 0,
+		33 => 1,
+		34 => 2,
+		35 => 3,
+		36 => 4,
+		37 => 5,
+		38 => 6,
+		39 => 7,
+		40 => 8,
+	];
+	public const MATERIAL_REDUCER_OUTPUT = [
+		41 => 0,
+		42 => 1,
+		43 => 2,
+		44 => 3,
+		45 => 4,
+		46 => 5,
+		47 => 6,
+		48 => 7,
+		49 => 8,
+	];
+	public const CREATED_ITEM_OUTPUT = 50;
+}