diff --git a/src/inventory/BaseInventory.php b/src/inventory/BaseInventory.php
index 6154bcb900..433fcbf879 100644
--- a/src/inventory/BaseInventory.php
+++ b/src/inventory/BaseInventory.php
@@ -108,13 +108,23 @@ abstract class BaseInventory implements Inventory{
 		$this->onContentChange($oldContents);
 	}
 
+	/**
+	 * Helper for utility functions which search the inventory.
+	 * TODO: make this abstract instead of providing a slow default implementation (BC break)
+	 */
+	protected function getMatchingItemCount(int $slot, Item $test, bool $checkDamage, bool $checkTags) : int{
+		$item = $this->getItem($slot);
+		return $item->equals($test, $checkDamage, $checkTags) ? $item->getCount() : 0;
+	}
+
 	public function contains(Item $item) : bool{
 		$count = max(1, $item->getCount());
 		$checkDamage = !$item->hasAnyDamageValue();
 		$checkTags = $item->hasNamedTag();
-		foreach($this->getContents() as $i){
-			if($item->equals($i, $checkDamage, $checkTags)){
-				$count -= $i->getCount();
+		for($i = 0, $size = $this->getSize(); $i < $size; $i++){
+			$slotCount = $this->getMatchingItemCount($i, $item, $checkDamage, $checkTags);
+			if($slotCount > 0){
+				$count -= $slotCount;
 				if($count <= 0){
 					return true;
 				}
@@ -128,9 +138,9 @@ abstract class BaseInventory implements Inventory{
 		$slots = [];
 		$checkDamage = !$item->hasAnyDamageValue();
 		$checkTags = $item->hasNamedTag();
-		foreach($this->getContents() as $index => $i){
-			if($item->equals($i, $checkDamage, $checkTags)){
-				$slots[$index] = $i;
+		for($i = 0, $size = $this->getSize(); $i < $size; $i++){
+			if($this->getMatchingItemCount($i, $item, $checkDamage, $checkTags) > 0){
+				$slots[$i] = $this->getItem($i);
 			}
 		}
 
@@ -142,9 +152,10 @@ abstract class BaseInventory implements Inventory{
 		$checkDamage = $exact || !$item->hasAnyDamageValue();
 		$checkTags = $exact || $item->hasNamedTag();
 
-		foreach($this->getContents() as $index => $i){
-			if($item->equals($i, $checkDamage, $checkTags) && ($i->getCount() === $count || (!$exact && $i->getCount() > $count))){
-				return $index;
+		for($i = 0, $size = $this->getSize(); $i < $size; $i++){
+			$slotCount = $this->getMatchingItemCount($i, $item, $checkDamage, $checkTags);
+			if($slotCount > 0 && ($slotCount === $count || (!$exact && $slotCount > $count))){
+				return $i;
 			}
 		}
 
@@ -177,11 +188,9 @@ abstract class BaseInventory implements Inventory{
 			if($this->isSlotEmpty($i)){
 				$count -= $maxStackSize;
 			}else{
-				$slot = $this->getItem($i);
-				if($item->canStackWith($slot)){
-					if(($diff = $maxStackSize - $slot->getCount()) > 0){
-						$count -= $diff;
-					}
+				$slotCount = $this->getMatchingItemCount($i, $item, true, true);
+				if($slotCount > 0 && ($diff = $maxStackSize - $slotCount) > 0){
+					$count -= $diff;
 				}
 			}
 
@@ -226,12 +235,16 @@ abstract class BaseInventory implements Inventory{
 				$emptySlots[] = $i;
 				continue;
 			}
-			$slotItem = $this->getItem($i);
+			$slotCount = $this->getMatchingItemCount($i, $newItem, true, true);
+			if($slotCount === 0){
+				continue;
+			}
 
-			if($newItem->canStackWith($slotItem) && $slotItem->getCount() < $maxStackSize){
-				$amount = min($maxStackSize - $slotItem->getCount(), $newItem->getCount());
+			if($slotCount < $maxStackSize){
+				$amount = min($maxStackSize - $slotCount, $newItem->getCount());
 				if($amount > 0){
 					$newItem->setCount($newItem->getCount() - $amount);
+					$slotItem = $this->getItem($i);
 					$slotItem->setCount($slotItem->getCount() + $amount);
 					$this->setItem($i, $slotItem);
 					if($newItem->getCount() <= 0){
@@ -261,20 +274,20 @@ abstract class BaseInventory implements Inventory{
 		$checkDamage = !$item->hasAnyDamageValue();
 		$checkTags = $item->hasNamedTag();
 
-		foreach($this->getContents() as $index => $i){
-			if($item->equals($i, $checkDamage, $checkTags)){
-				$this->clear($index);
+		for($i = 0, $size = $this->getSize(); $i < $size; $i++){
+			if($this->getMatchingItemCount($i, $item, $checkDamage, $checkTags) > 0){
+				$this->clear($i);
 			}
 		}
 	}
 
 	public function removeItem(Item ...$slots) : array{
-		/** @var Item[] $itemSlots */
+		/** @var Item[] $searchItems */
 		/** @var Item[] $slots */
-		$itemSlots = [];
+		$searchItems = [];
 		foreach($slots as $slot){
 			if(!$slot->isNull()){
-				$itemSlots[] = clone $slot;
+				$searchItems[] = clone $slot;
 			}
 		}
 
@@ -282,26 +295,28 @@ abstract class BaseInventory implements Inventory{
 			if($this->isSlotEmpty($i)){
 				continue;
 			}
-			$item = $this->getItem($i);
 
-			foreach($itemSlots as $index => $slot){
-				if($slot->equals($item, !$slot->hasAnyDamageValue(), $slot->hasNamedTag())){
-					$amount = min($item->getCount(), $slot->getCount());
-					$slot->setCount($slot->getCount() - $amount);
-					$item->setCount($item->getCount() - $amount);
-					$this->setItem($i, $item);
-					if($slot->getCount() <= 0){
-						unset($itemSlots[$index]);
+			foreach($searchItems as $index => $search){
+				$slotCount = $this->getMatchingItemCount($i, $search, !$search->hasAnyDamageValue(), $search->hasNamedTag());
+				if($slotCount > 0){
+					$amount = min($slotCount, $search->getCount());
+					$search->setCount($search->getCount() - $amount);
+
+					$slotItem = $this->getItem($i);
+					$slotItem->setCount($slotItem->getCount() - $amount);
+					$this->setItem($i, $slotItem);
+					if($search->getCount() <= 0){
+						unset($searchItems[$index]);
 					}
 				}
 			}
 
-			if(count($itemSlots) === 0){
+			if(count($searchItems) === 0){
 				break;
 			}
 		}
 
-		return $itemSlots;
+		return $searchItems;
 	}
 
 	public function clear(int $index) : void{
diff --git a/src/inventory/SimpleInventory.php b/src/inventory/SimpleInventory.php
index 19fbdbb17c..c1f352b7b7 100644
--- a/src/inventory/SimpleInventory.php
+++ b/src/inventory/SimpleInventory.php
@@ -84,6 +84,11 @@ class SimpleInventory extends BaseInventory{
 		}
 	}
 
+	protected function getMatchingItemCount(int $slot, Item $test, bool $checkDamage, bool $checkTags) : int{
+		$slotItem = $this->slots[$slot];
+		return $slotItem !== null && $slotItem->equals($test, $checkDamage, $checkTags) ? $slotItem->getCount() : 0;
+	}
+
 	public function isSlotEmpty(int $index) : bool{
 		return $this->slots[$index] === null || $this->slots[$index]->isNull();
 	}