diff --git a/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/InventoryUpdatedEvent.java b/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/InventoryUpdatedEvent.java
index d0bd8eb..0e6fb45 100644
--- a/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/InventoryUpdatedEvent.java
+++ b/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/InventoryUpdatedEvent.java
@@ -6,12 +6,10 @@ import org.bukkit.inventory.ItemStack;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-// TODO: better solution?
-
 /**
  * An event that is called after the {@link VirtualInventory} has been updated.
  */
-public class InventoryUpdatedEvent extends ItemUpdateEvent {
+public class InventoryUpdatedEvent extends UpdateEvent {
     
     /**
      * Creates a new {@link ItemUpdateEvent}.
diff --git a/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/ItemUpdateEvent.java b/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/ItemUpdateEvent.java
index 46c5cd7..b1e8bd9 100644
--- a/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/ItemUpdateEvent.java
+++ b/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/ItemUpdateEvent.java
@@ -11,6 +11,8 @@ import org.jetbrains.annotations.Nullable;
  */
 public class ItemUpdateEvent extends UpdateEvent {
     
+    private boolean cancelled;
+    
     /**
      * Creates a new {@link ItemUpdateEvent}.
      *
@@ -29,7 +31,16 @@ public class ItemUpdateEvent extends UpdateEvent {
         super(virtualInventory, slot, updateReason, previousItemStack, newItemStack);
     }
     
-    private boolean cancelled;
+    /**
+     * Change the {@link ItemStack} that will appear in the {@link VirtualInventory}
+     * to a different one.
+     *
+     * @param newItemStack The {@link ItemStack} to appear in the {@link VirtualInventory}
+     *                     if the {@link ItemUpdateEvent} is not cancelled.
+     */
+    public void setNewItemStack(@Nullable ItemStack newItemStack) {
+        this.newItemStack = newItemStack;
+    }
     
     /**
      * Gets the cancellation state of this event.
diff --git a/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/UpdateEvent.java b/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/UpdateEvent.java
index ef1d062..12d6758 100644
--- a/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/UpdateEvent.java
+++ b/InvUI/src/main/java/de/studiocode/invui/virtualinventory/event/UpdateEvent.java
@@ -9,10 +9,10 @@ import org.jetbrains.annotations.Nullable;
 abstract class UpdateEvent {
     
     private final VirtualInventory virtualInventory;
-    private final ItemStack previousItemStack;
     private final UpdateReason updateReason;
     private final int slot;
-    private ItemStack newItemStack;
+    private final ItemStack previousItemStack;
+    protected ItemStack newItemStack;
     
     /**
      * Creates a new {@link ItemUpdateEvent}.
@@ -32,8 +32,8 @@ abstract class UpdateEvent {
         this.virtualInventory = virtualInventory;
         this.slot = slot;
         this.updateReason = updateReason;
-        this.previousItemStack = previousItemStack;
-        this.newItemStack = newItemStack;
+        this.previousItemStack = previousItemStack != null ? previousItemStack.clone() : null;
+        this.newItemStack = newItemStack != null ? newItemStack.clone() : null;
     }
     
     /**
@@ -55,7 +55,7 @@ abstract class UpdateEvent {
     }
     
     /**
-     * Gets the {@link ItemStack} that was there previously.
+     * Gets a clone of the {@link ItemStack} that was there previously.
      *
      * @return The {@link ItemStack}
      */
@@ -64,7 +64,7 @@ abstract class UpdateEvent {
     }
     
     /**
-     * The new {@link ItemStack} that will be there if the event isn't cancelled.
+     * Gets clone of the new {@link ItemStack} that will be there if the event isn't cancelled.
      *
      * @return The new {@link ItemStack}
      */
@@ -72,17 +72,6 @@ abstract class UpdateEvent {
         return newItemStack;
     }
     
-    /**
-     * Change the {@link ItemStack} that will appear in the {@link VirtualInventory}
-     * to a different one.
-     *
-     * @param newItemStack The {@link ItemStack} to appear in the {@link VirtualInventory}
-     *                     if the {@link ItemUpdateEvent} is not cancelled.
-     */
-    public void setNewItemStack(@Nullable ItemStack newItemStack) {
-        this.newItemStack = newItemStack;
-    }
-    
     /**
      * Gets the slot that is affected.
      *