diff --git a/src/pocketmine/inventory/transaction/CraftingTransaction.php b/src/pocketmine/inventory/transaction/CraftingTransaction.php
index f98d38fb9..0b4fa7fd0 100644
--- a/src/pocketmine/inventory/transaction/CraftingTransaction.php
+++ b/src/pocketmine/inventory/transaction/CraftingTransaction.php
@@ -61,8 +61,8 @@ class CraftingTransaction extends InventoryTransaction{
 
 		if($this->inputs[$y][$x]->isNull()){
 			$this->inputs[$y][$x] = clone $item;
-		}else{
-			throw new \RuntimeException("Input $index has already been set");
+		}elseif(!$this->inputs[$y][$x]->equals($item)){
+			throw new \RuntimeException("Input $index has already been set and does not match the current item (expected " . $this->inputs[$y][$x] . ", got " . $item . ")");
 		}
 	}
 
@@ -76,8 +76,8 @@ class CraftingTransaction extends InventoryTransaction{
 
 		if($this->secondaryOutputs[$y][$x]->isNull()){
 			$this->secondaryOutputs[$y][$x] = clone $item;
-		}else{
-			throw new \RuntimeException("Output $index has already been set");
+		}elseif(!$this->secondaryOutputs[$y][$x]->equals($item)){
+			throw new \RuntimeException("Output $index has already been set and does not match the current item (expected " . $this->secondaryOutputs[$y][$x] . ", got " . $item . ")");
 		}
 	}
 
@@ -88,8 +88,8 @@ class CraftingTransaction extends InventoryTransaction{
 	public function setPrimaryOutput(Item $item) : void{
 		if($this->primaryOutput === null){
 			$this->primaryOutput = clone $item;
-		}else{
-			throw new \RuntimeException("Primary result item has already been set");
+		}elseif(!$this->primaryOutput->equals($item)){
+			throw new \RuntimeException("Primary result item has already been set and does not match the current item (expected " . $this->primaryOutput . ", got " . $item . ")");
 		}
 	}