diff --git a/src/main/java/owmii/powah/lib/logistics/inventory/ItemStackHandler.java b/src/main/java/owmii/powah/lib/logistics/inventory/ItemStackHandler.java
index 2158fa4..f0df002 100644
--- a/src/main/java/owmii/powah/lib/logistics/inventory/ItemStackHandler.java
+++ b/src/main/java/owmii/powah/lib/logistics/inventory/ItemStackHandler.java
@@ -78,7 +78,8 @@ public ItemStack insertItem(int slot, @NotNull ItemStack stack, boolean simulate
 
         if (!simulate) {
             if (existing.isEmpty()) {
-                this.stacks.set(slot, reachedLimit ? ItemStackHandlerHelper.copyStackWithSize(stack, limit) : stack);
+                // We must always copy the stack because onContentsChanged might change it, messing with our later use.
+                this.stacks.set(slot, reachedLimit ? ItemStackHandlerHelper.copyStackWithSize(stack, limit) : stack.copy());
             } else {
                 existing.grow(reachedLimit ? limit : stack.getCount());
             }