diff --git a/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftAbstractInventoryView.java b/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftAbstractInventoryView.java
index 48c0a876fd54..876eda8d82b6 100644
--- a/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftAbstractInventoryView.java
+++ b/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftAbstractInventoryView.java
@@ -56,16 +56,23 @@ public Inventory getInventory(final int rawSlot) {
     }
 
     public Inventory mapValidSlotToInventory(final int rawSlot) {
-        if (rawSlot < this.getTopInventory().getSize()) {
+        if (rawSlot < this.getTopSlots()) {
             return this.getTopInventory();
         } else {
             return this.getBottomInventory();
         }
     }
 
+    // The number of raw slots the top inventory occupies in the open menu. This is
+    // usually just its size, but a view can override it when the menu renders fewer
+    // slots than the inventory reports (e.g. a player inventory shown as a chest).
+    public int getTopSlots() {
+        return this.getTopInventory().getSize();
+    }
+
     @Override
     public int convertSlot(final int rawSlot) {
-        int numInTop = this.getTopInventory().getSize();
+        int numInTop = this.getTopSlots();
         // Index from the top inventory as having slots from [0,size]
         if (rawSlot < numInTop) {
             return rawSlot;
@@ -132,7 +139,7 @@ public int convertSlot(final int rawSlot) {
     @Override
     public InventoryType.SlotType getSlotType(final int slot) {
         InventoryType.SlotType type = InventoryType.SlotType.CONTAINER;
-        if (slot >= 0 && slot < this.getTopInventory().getSize()) {
+        if (slot >= 0 && slot < this.getTopSlots()) {
             switch (this.getType()) {
                 case BLAST_FURNACE:
                 case FURNACE:
@@ -229,7 +236,7 @@ public void close() {
 
     @Override
     public int countSlots() {
-        return this.getTopInventory().getSize() + this.getBottomInventory().getSize();
+        return this.getTopSlots() + this.getBottomInventory().getSize();
     }
 
     @Override
diff --git a/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftContainer.java b/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftContainer.java
index 2f41a92465b9..fe6f9da3dfe5 100644
--- a/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftContainer.java
+++ b/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftContainer.java
@@ -72,6 +72,18 @@ public InventoryType getType() {
                 return inventory.getType();
             }
 
+            @Override
+            public int getTopSlots() {
+                // A player inventory shown inside a container is laid out as a generic
+                // chest (whole rows of 9), so the armour and off-hand slots that
+                // getSize() counts are not rendered. Use the number of slots actually
+                // laid out so the raw-slot mapping matches the open menu.
+                if (inventory.getType() == InventoryType.PLAYER) {
+                    return (inventory.getSize() / 9) * 9;
+                }
+                return inventory.getSize();
+            }
+
             // Paper start
             @Override
             public net.kyori.adventure.text.Component title() {