diff --git a/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUI.kt b/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUI.kt
index 680be565..d29d3909 100644
--- a/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUI.kt
+++ b/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUI.kt
@@ -27,14 +27,14 @@ fun HumanEntity.openGUI(gui: InventoryGUI<*>, page: Int? = null): InventoryView?
 
 class InventoryGUIHolder(kSpigot: KSpigot) : AutoCloseable {
 
-    private val registered = HashSet<InventoryGUI<*>>()
+    private val registered = HashSet<InventoryGUI<ForInventory>>()
 
-    fun register(inventoryGUI: InventoryGUI<*>) {
-        registered += inventoryGUI
+    fun register(inventoryGUI: InventoryGUI<ForInventory>) {
+        registered.add(inventoryGUI)
     }
 
-    fun unregister(inventoryGUI: InventoryGUI<*>) {
-        registered -= inventoryGUI
+    fun unregister(inventoryGUI: InventoryGUI<ForInventory>) {
+        registered.remove(inventoryGUI)
     }
 
     init {
@@ -77,7 +77,7 @@ class InventoryGUIData<T : ForInventory>(
         val plugin: KSpigot,
         val inventoryType: InventoryType<T>,
         val title: String?,
-        val pages: Map<Int, InventoryGUIPage>
+        val pages: Map<Int, InventoryGUIPage<T>>
 )
 
 abstract class InventoryGUI<T : ForInventory>(
@@ -94,8 +94,10 @@ abstract class InventoryGUI<T : ForInventory>(
 
     abstract operator fun set(slot: InventorySlotCompound<T>, value: ItemStack)
 
-    fun register() = data.plugin.inventoryGUIHolder.register(this)
-    fun unregister() = data.plugin.inventoryGUIHolder.unregister(this)
+    @Suppress("UNCHECKED_CAST")
+    fun register() = data.plugin.inventoryGUIHolder.register(this as InventoryGUI<ForInventory>)
+    @Suppress("UNCHECKED_CAST")
+    fun unregister() = data.plugin.inventoryGUIHolder.unregister(this as InventoryGUI<ForInventory>)
 
 }
 
@@ -165,8 +167,8 @@ class InventoryGUIShared<T : ForInventory>(
 
 }
 
-class InventoryGUIPage(
-        val slots: Map<Int, InventoryGUISlot>,
+class InventoryGUIPage<T : ForInventory>(
+        val slots: Map<Int, InventoryGUISlot<T>>,
         transitionTo: InventoryGUIPageChangeEffect?,
         transitionFrom: InventoryGUIPageChangeEffect?
 ) {
diff --git a/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUIBuilder.kt b/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUIBuilder.kt
index 9447511d..78a2053c 100644
--- a/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUIBuilder.kt
+++ b/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUIBuilder.kt
@@ -17,7 +17,7 @@ class InventoryGUIBuilder<T : ForInventory>(
 
     var title: String = ""
 
-    private val guiSlots = HashMap<Int, InventoryGUIPage>()
+    private val guiSlots = HashMap<Int, InventoryGUIPage<T>>()
 
     /**
      *
@@ -35,7 +35,7 @@ class InventoryGUIPageBuilder<T : ForInventory>(
         val page: Int
 ) {
 
-    private val guiSlots = HashMap<Int, InventoryGUISlot>()
+    private val guiSlots = HashMap<Int, InventoryGUISlot<T>>()
 
     var transitionTo: InventoryGUIPageChangeEffect? = null
     var transitionFrom: InventoryGUIPageChangeEffect? = null
@@ -98,7 +98,7 @@ class InventoryGUIPageBuilder<T : ForInventory>(
             onChange
         ))
 
-    private fun slots(slots: InventorySlotCompound<T>, element: InventoryGUISlot)
+    private fun slots(slots: InventorySlotCompound<T>, element: InventoryGUISlot<T>)
         = slots.withInvType(type).forEach { curSlot ->
             curSlot.realSlotIn(type.dimensions)?.let { guiSlots[it] = element  }
         }
diff --git a/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUIElements.kt b/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUIElements.kt
index 7fedfd27..7e3368a0 100644
--- a/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUIElements.kt
+++ b/src/main/kotlin/net/axay/kspigot/inventory/InventoryGUIElements.kt
@@ -2,8 +2,8 @@ package net.axay.kspigot.inventory
 
 import org.bukkit.inventory.ItemStack
 
-interface InventoryGUISlot {
-    fun onClick(clickEvent: InventoryGUIClickEvent)
+interface InventoryGUISlot<T : ForInventory> {
+    fun onClick(clickEvent: InventoryGUIClickEvent<T>)
 }
 
 // ELEMENT
@@ -12,60 +12,60 @@ class InventoryGUIElementData(
         val itemStack: ItemStack
 )
 
-abstract class InventoryGUIElement(
+abstract class InventoryGUIElement<T : ForInventory>(
         val inventoryGUIElementData: InventoryGUIElementData
-) : InventoryGUISlot
+) : InventoryGUISlot<T>
 
 // Element implementations
 
-open class InventoryGUIButton(
+open class InventoryGUIButton<T : ForInventory>(
         inventoryGUIElementData: InventoryGUIElementData,
-        val action: (InventoryGUIClickEvent) -> Unit,
-) : InventoryGUIElement(inventoryGUIElementData) {
+        val action: (InventoryGUIClickEvent<T>) -> Unit,
+) : InventoryGUIElement<T>(inventoryGUIElementData) {
 
-    override fun onClick(clickEvent: InventoryGUIClickEvent) {
+    override fun onClick(clickEvent: InventoryGUIClickEvent<T>) {
         clickEvent.bukkitEvent.isCancelled = true
         action(clickEvent)
     }
 
 }
 
-class InventoryGUIPlaceholder(
+class InventoryGUIPlaceholder<T : ForInventory>(
         inventoryGUIElementData: InventoryGUIElementData
-) : InventoryGUIElement(inventoryGUIElementData) {
+) : InventoryGUIElement<T>(inventoryGUIElementData) {
 
-    override fun onClick(clickEvent: InventoryGUIClickEvent) {
+    override fun onClick(clickEvent: InventoryGUIClickEvent<T>) {
         clickEvent.bukkitEvent.isCancelled = true
     }
 
 }
 
-class InventoryGUIButtonPageChange(
+class InventoryGUIButtonPageChange<T : ForInventory>(
         inventoryGUIElementData: InventoryGUIElementData,
         calculator: InventoryGUIPageChangeCalculator,
-        onChange: ((InventoryGUIClickEvent) -> Unit)?
+        onChange: ((InventoryGUIClickEvent<T>) -> Unit)?
 )
-    : InventoryGUIButton(inventoryGUIElementData, {
-        it.gui.currentPage?.let { currentPageInt ->
+    : InventoryGUIButton<T>(inventoryGUIElementData, {
 
-            val newPageInt = calculator.calculateNewPage(currentPageInt, it.gui.data.pages.keys)
-            if (newPageInt != null) {
+        val currentPage = it.gui.currentPage
 
-                onChange?.invoke(it)
+        val newPageInt = calculator.calculateNewPage(currentPage, it.gui.data.pages.keys)
+        if (newPageInt != null) {
 
-                val pageChanger
-                        = (it.gui.data.pages[newPageInt]?.pageChangerTo ?: it.gui.data.pages[currentPageInt]?.pageChangerFrom)
-                        ?: InventoryGUIPageChanger(InventoryGUIPageChangeEffect.INSTANT)
+            onChange?.invoke(it)
 
-                pageChanger.changePage(it.gui, currentPageInt, newPageInt)
+            val pageChanger
+                    = (it.gui.data.pages[newPageInt]?.pageChangerTo ?: it.gui.data.pages[currentPage]?.pageChangerFrom)
+                    ?: InventoryGUIPageChanger(InventoryGUIPageChangeEffect.INSTANT)
 
-            }
+            pageChanger.changePage(it.gui, currentPage, newPageInt)
 
         }
+
     })
 
 // FREE SLOT
 
-class InventoryGUIFreeSlot : InventoryGUISlot {
-    override fun onClick(clickEvent: InventoryGUIClickEvent) { /* do nothing */ }
+class InventoryGUIFreeSlot<T : ForInventory> : InventoryGUISlot<T> {
+    override fun onClick(clickEvent: InventoryGUIClickEvent<T>) { /* do nothing */ }
 }
\ No newline at end of file