diff --git a/autoloads/inventory_manager.gd b/autoloads/inventory_manager.gd
index c539b00..a18029b 100644
--- a/autoloads/inventory_manager.gd
+++ b/autoloads/inventory_manager.gd
@@ -37,7 +37,7 @@ func _unhandled_input(event: InputEvent) -> void:
 		add_to_inventory.emit("003", 1)
 
 
-func _find_first_stack(item_resource: DBItemResource, item_id: String) -> bool:
+func _find_first_available_stack(item_resource: DBItemResource, item_id: String) -> bool:
 	return (
 		item_resource.id == item_id and
 		item_resource.amount < item_resource.max_stack_size
@@ -45,33 +45,43 @@ func _find_first_stack(item_resource: DBItemResource, item_id: String) -> bool:
 
 
 func _on_add_to_inventory(item_id: String, amount: int = 1) -> void:
+	if not DBItems.data.get(item_id):
+		printerr("Cannot add item, ", item_id, ", to inventory. Could not find item within DBItems.data.")
+		return
+	if amount < 1:
+		printerr("Cannot add item, ", item_id, ", to inventory. Amount to add cannot be less then 1.")
+		return
+
 	var item_resource: DBItemResource = DBItems.data[item_id]
 
-	# The logic below is a mess and needs to be reworked
+	# This logic seems overly complicated and is a mess.
+	#   Should look into fixing/simplifying this in the future
 	var amount_remaining: int = amount
 	while amount_remaining > 0:
-		var first_stack_index: int = inventory.find_custom(_find_first_stack.bind(item_id))
+		var first_stack_index: int = inventory.find_custom(_find_first_available_stack.bind(item_id))
 
 		if first_stack_index == -1 and inventory.size() < max_inventory_items:
-			inventory.append(item_resource)
+			var stack_resource: DBItemResource = item_resource.duplicate()
+			inventory.append(stack_resource)
 
-			if amount_remaining <= item_resource.max_stack_size:
+			if amount_remaining <= stack_resource.max_stack_size:
 				inventory[-1].amount += amount_remaining
 				amount_remaining = 0
 			else:
-				inventory[-1].amount = item_resource.max_stack_size
-				amount_remaining -= item_resource.max_stack_size
+				inventory[-1].amount = stack_resource.max_stack_size
+				amount_remaining -= stack_resource.max_stack_size
 
 			item_added.emit(item_id, amount - amount_remaining)
 		elif first_stack_index > -1:
-			var current_amount: int = inventory[first_stack_index].amount
+			var stack_resource: DBItemResource = inventory[first_stack_index]
+			var current_amount: int = stack_resource.amount
 			var total_amount: int = current_amount + amount_remaining
-			if item_resource.max_stack_size - total_amount < 0:
-				inventory[first_stack_index].amount += amount_remaining
+			if total_amount < stack_resource.max_stack_size: # Stack not full and can hold
+				inventory[first_stack_index].amount = total_amount
 				amount_remaining = 0
 			else:
-				inventory[first_stack_index].amount = item_resource.max_stack_size
-				amount_remaining -= item_resource.max_stack_size
+				inventory[first_stack_index].amount = stack_resource.max_stack_size
+				amount_remaining -= stack_resource.max_stack_size
 
 			item_added.emit(item_id, amount - amount_remaining)
 
diff --git a/scenes/ui/inventory/inventory.gd b/scenes/ui/inventory/inventory.gd
index fa7d08e..12c5390 100644
--- a/scenes/ui/inventory/inventory.gd
+++ b/scenes/ui/inventory/inventory.gd
@@ -47,7 +47,7 @@ func refresh_inventory_grid() -> void:
 	for item: DBItemResource in InventoryManager.inventory:
 		create_item_cell(item)
 
-	var empty_cells: int = InventoryManager.max_inventory_items - inventory_resource.inventory.size()
+	var empty_cells: int = InventoryManager.max_inventory_items - InventoryManager.inventory.size()
 	for _i: int in range(empty_cells):
 		create_item_cell(null)
 
@@ -63,8 +63,11 @@ func toggle_inventory() -> void:
 		InventoryManager.inventory_closed.emit()
 		get_tree().paused = false
 
+## Add any items from the existing inventory resource
 func update_inventory_with_resource() -> void:
-	# Add any items from the existing inventory resource
+	if inventory_resource == null:
+		return
+
 	for item_resource: DBItemResource in inventory_resource.inventory:
 		InventoryManager.add_to_inventory.emit(item_resource.id, item_resource.amount)