diff --git a/src/pocketmine/inventory/transaction/CraftingTransaction.php b/src/pocketmine/inventory/transaction/CraftingTransaction.php
index 1755f8d36..599a27829 100644
--- a/src/pocketmine/inventory/transaction/CraftingTransaction.php
+++ b/src/pocketmine/inventory/transaction/CraftingTransaction.php
@@ -59,6 +59,10 @@ class CraftingTransaction extends InventoryTransaction{
 		$y = (int) ($index / $this->gridSize);
 		$x = $index % $this->gridSize;
 
+		if(!isset($this->inputs[$y][$x])){
+			return;
+		}
+
 		if($this->inputs[$y][$x]->isNull()){
 			$this->inputs[$y][$x] = clone $item;
 		}elseif(!$this->inputs[$y][$x]->equals($item)){
@@ -74,6 +78,10 @@ class CraftingTransaction extends InventoryTransaction{
 		$y = (int) ($index / $this->gridSize);
 		$x = $index % $this->gridSize;
 
+		if(!isset($this->secondaryOutputs[$y][$x])){
+			return;
+		}
+
 		if($this->secondaryOutputs[$y][$x]->isNull()){
 			$this->secondaryOutputs[$y][$x] = clone $item;
 		}elseif(!$this->secondaryOutputs[$y][$x]->equals($item)){