diff --git a/InvUI/src/main/java/de/studiocode/invui/virtualinventory/VirtualInventory.java b/InvUI/src/main/java/de/studiocode/invui/virtualinventory/VirtualInventory.java
index 134f8b9..1627bf2 100644
--- a/InvUI/src/main/java/de/studiocode/invui/virtualinventory/VirtualInventory.java
+++ b/InvUI/src/main/java/de/studiocode/invui/virtualinventory/VirtualInventory.java
@@ -411,7 +411,8 @@ public class VirtualInventory implements ConfigurationSerializable {
                     items[slot] = newItemStack;
                     notifyWindows();
                     
-                    return itemStack.getAmount() - (newItemStack.getAmount() - currentAmount);
+                    int newAmount = newItemStack != null ? newItemStack.getAmount() : 0;
+                    return itemStack.getAmount() - (newAmount - currentAmount);
                 }
             }
         }