diff --git a/eco-api/src/main/java/com/willfp/eco/core/gui/slot/SlotBuilder.java b/eco-api/src/main/java/com/willfp/eco/core/gui/slot/SlotBuilder.java
index 0646fd2b..caed0b72 100644
--- a/eco-api/src/main/java/com/willfp/eco/core/gui/slot/SlotBuilder.java
+++ b/eco-api/src/main/java/com/willfp/eco/core/gui/slot/SlotBuilder.java
@@ -2,6 +2,7 @@ package com.willfp.eco.core.gui.slot;
 
 import com.willfp.eco.core.gui.slot.functional.SlotHandler;
 import com.willfp.eco.core.gui.slot.functional.SlotModifier;
+import com.willfp.eco.core.gui.slot.functional.SlotUpdater;
 import org.bukkit.event.inventory.InventoryClickEvent;
 import org.jetbrains.annotations.NotNull;
 
@@ -106,8 +107,23 @@ public interface SlotBuilder {
      *
      * @param modifier The modifier.
      * @return The builder.
+     * @deprecated Use {@link SlotBuilder#setUpdater(SlotUpdater)} instead.
      */
-    SlotBuilder setModifier(@NotNull SlotModifier modifier);
+    @Deprecated
+    default SlotBuilder setModifier(@NotNull SlotModifier modifier) {
+        return setUpdater((player, menu, previous) -> {
+            modifier.modify(player, menu, previous);
+            return previous;
+        });
+    }
+
+    /**
+     * Set the ItemStack updater.
+     *
+     * @param updater The updater.
+     * @return The builder.
+     */
+    SlotBuilder setUpdater(@NotNull SlotUpdater updater);
 
     /**
      * Set slot to be a captive slot.
diff --git a/eco-api/src/main/java/com/willfp/eco/core/gui/slot/functional/SlotModifier.java b/eco-api/src/main/java/com/willfp/eco/core/gui/slot/functional/SlotModifier.java
index f9a2bbe6..3b3df359 100644
--- a/eco-api/src/main/java/com/willfp/eco/core/gui/slot/functional/SlotModifier.java
+++ b/eco-api/src/main/java/com/willfp/eco/core/gui/slot/functional/SlotModifier.java
@@ -7,8 +7,11 @@ import org.jetbrains.annotations.NotNull;
 
 /**
  * Interface to run on slot modify.
+ *
+ * @deprecated Use {@link SlotUpdater} instead.
  */
 @FunctionalInterface
+@Deprecated
 public interface SlotModifier {
     /**
      * Performs this operation on the given arguments.
diff --git a/eco-api/src/main/java/com/willfp/eco/core/gui/slot/functional/SlotUpdater.java b/eco-api/src/main/java/com/willfp/eco/core/gui/slot/functional/SlotUpdater.java
new file mode 100644
index 00000000..83c51ba3
--- /dev/null
+++ b/eco-api/src/main/java/com/willfp/eco/core/gui/slot/functional/SlotUpdater.java
@@ -0,0 +1,24 @@
+package com.willfp.eco.core.gui.slot.functional;
+
+import com.willfp.eco.core.gui.menu.Menu;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Interface to run on slot update.
+ */
+@FunctionalInterface
+public interface SlotUpdater {
+    /**
+     * Performs this operation on the given arguments.
+     *
+     * @param player   The player.
+     * @param menu     The menu.
+     * @param previous The previous ItemStack.
+     * @return The new ItemStack.
+     */
+    ItemStack update(@NotNull Player player,
+                     @NotNull Menu menu,
+                     @NotNull ItemStack previous);
+}
diff --git a/eco-api/src/main/kotlin/com/willfp/eco/core/gui/GUIHelpers.kt b/eco-api/src/main/kotlin/com/willfp/eco/core/gui/GUIHelpers.kt
index 57d7da19..cdcf92f9 100644
--- a/eco-api/src/main/kotlin/com/willfp/eco/core/gui/GUIHelpers.kt
+++ b/eco-api/src/main/kotlin/com/willfp/eco/core/gui/GUIHelpers.kt
@@ -43,10 +43,18 @@ fun SlotBuilder.onMiddleClick(action: (InventoryClickEvent, Slot, Menu) -> Unit)
 
 /**
  * @see SlotBuilder.setModifier
+ * @deprecated Use SlotUpdater instead.
  */
+@Deprecated("Use SlotUpdater instead")
 fun SlotBuilder.setModifier(action: (Player, Menu, ItemStack) -> Unit): SlotBuilder =
     this.setModifier { a, b, c -> action(a, b, c) }
 
+/**
+ * @see SlotBuilder.setUpdater
+ */
+fun SlotBuilder.setUpdater(action: (Player, Menu, ItemStack) -> ItemStack): SlotBuilder =
+    this.setUpdater { a, b, c -> action(a, b, c) }
+
 /**
  * Kotlin builder for slots.
  */
diff --git a/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoCaptiveSlot.kt b/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoCaptiveSlot.kt
index ba776540..cb9ada47 100644
--- a/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoCaptiveSlot.kt
+++ b/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoCaptiveSlot.kt
@@ -12,7 +12,7 @@ class EcoCaptiveSlot(
     allowMovingItem,
     allowMovingItem,
     allowMovingItem,
-    { _, _, _ -> }
+    { _, _, prev -> prev }
 ) {
     override fun isCaptive(): Boolean {
         return true
diff --git a/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoFillerSlot.kt b/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoFillerSlot.kt
index b43764fb..307ab85c 100644
--- a/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoFillerSlot.kt
+++ b/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoFillerSlot.kt
@@ -9,5 +9,5 @@ class EcoFillerSlot(itemStack: ItemStack) : EcoSlot(
     { _, _, _ -> },
     { _, _, _ -> },
     { _, _, _ -> },
-    { _, _, _ -> }
+    { _, _, prev -> prev }
 )
\ No newline at end of file
diff --git a/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoSlot.kt b/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoSlot.kt
index fd2a005f..27fefd90 100644
--- a/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoSlot.kt
+++ b/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoSlot.kt
@@ -3,8 +3,8 @@ package com.willfp.eco.internal.gui.slot
 import com.willfp.eco.core.gui.menu.Menu
 import com.willfp.eco.core.gui.slot.Slot
 import com.willfp.eco.core.gui.slot.functional.SlotHandler
-import com.willfp.eco.core.gui.slot.functional.SlotModifier
 import com.willfp.eco.core.gui.slot.functional.SlotProvider
+import com.willfp.eco.core.gui.slot.functional.SlotUpdater
 import com.willfp.eco.internal.gui.menu.MenuHandler
 import org.bukkit.entity.Player
 import org.bukkit.event.inventory.ClickType
@@ -18,7 +18,7 @@ open class EcoSlot(
     private val onShiftLeftClick: SlotHandler,
     private val onShiftRightClick: SlotHandler,
     private val onMiddleClick: SlotHandler,
-    private val modifier: SlotModifier
+    private val updater: SlotUpdater
 ) : Slot {
 
     fun handleInventoryClick(
@@ -38,8 +38,7 @@ open class EcoSlot(
     override fun getItemStack(player: Player): ItemStack {
         val menu = MenuHandler.getMenu(player.openInventory.topInventory)!!
         val prev = provider.provide(player, menu)
-        modifier.modify(player, menu, prev)
-        return prev
+        return updater.update(player, menu, prev)
     }
 
     fun getItemStack(
@@ -47,8 +46,7 @@ open class EcoSlot(
         menu: Menu
     ): ItemStack {
         val prev = provider.provide(player, menu)
-        modifier.modify(player, menu, prev)
-        return prev
+        return updater.update(player, menu, prev)
     }
 
     override fun isCaptive(): Boolean {
diff --git a/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoSlotBuilder.kt b/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoSlotBuilder.kt
index 43707cf4..d4f7da97 100644
--- a/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoSlotBuilder.kt
+++ b/eco-core/core-backend/src/main/kotlin/com/willfp/eco/internal/gui/slot/EcoSlotBuilder.kt
@@ -3,12 +3,12 @@ package com.willfp.eco.internal.gui.slot
 import com.willfp.eco.core.gui.slot.Slot
 import com.willfp.eco.core.gui.slot.SlotBuilder
 import com.willfp.eco.core.gui.slot.functional.SlotHandler
-import com.willfp.eco.core.gui.slot.functional.SlotModifier
 import com.willfp.eco.core.gui.slot.functional.SlotProvider
+import com.willfp.eco.core.gui.slot.functional.SlotUpdater
 
 class EcoSlotBuilder(private val provider: SlotProvider) : SlotBuilder {
     private var captive = false
-    private var modifier: SlotModifier = SlotModifier { player, menu, _ -> provider.provide(player, menu) }
+    private var updater: SlotUpdater = SlotUpdater { player, menu, _ -> provider.provide(player, menu) }
 
     private var onLeftClick =
         SlotHandler { _, _, _ -> run { } }
@@ -51,8 +51,8 @@ class EcoSlotBuilder(private val provider: SlotProvider) : SlotBuilder {
         return this
     }
 
-    override fun setModifier(modifier: SlotModifier): SlotBuilder {
-        this.modifier = modifier
+    override fun setUpdater(updater: SlotUpdater): SlotBuilder {
+        this.updater = updater
         return this
     }
 
@@ -60,7 +60,7 @@ class EcoSlotBuilder(private val provider: SlotProvider) : SlotBuilder {
         return if (captive) {
             EcoCaptiveSlot(provider)
         } else {
-            EcoSlot(provider, onLeftClick, onRightClick, onShiftLeftClick, onShiftRightClick, onMiddleClick, modifier)
+            EcoSlot(provider, onLeftClick, onRightClick, onShiftLeftClick, onShiftRightClick, onMiddleClick, updater)
         }
     }
 }
\ No newline at end of file