diff --git a/pom.xml b/pom.xml
index d209470..c580a63 100644
--- a/pom.xml
+++ b/pom.xml
@@ -38,6 +38,12 @@
             <version>5.14.0</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-launcher</artifactId>
+            <version>1.14.0</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.mockbukkit.mockbukkit</groupId>
             <artifactId>mockbukkit-v1.21</artifactId>
diff --git a/src/main/java/net/tfminecraft/companionpets/PetsPlugin.java b/src/main/java/net/tfminecraft/companionpets/PetsPlugin.java
index f7b3dd7..159b2c3 100644
--- a/src/main/java/net/tfminecraft/companionpets/PetsPlugin.java
+++ b/src/main/java/net/tfminecraft/companionpets/PetsPlugin.java
@@ -252,7 +252,8 @@ private void reloadSettings(CommandSender sender) {
             return;
         }
         for (var player : Bukkit.getOnlinePlayers()) {
-            if (player.getOpenInventory().getTopInventory().getHolder() instanceof MenuHolder || player.getOpenInventory().getTopInventory().getHolder() instanceof net.tfminecraft.companionpets.staff.StaffMenuHolder) player.closeInventory();
+            var holder = player.getOpenInventory().getTopInventory().getHolder(false);
+            if (holder instanceof MenuHolder || holder instanceof net.tfminecraft.companionpets.staff.StaffMenuHolder) player.closeInventory();
         }
         actions.clearInteractions();
         actions.holograms().clear();
diff --git a/src/main/java/net/tfminecraft/companionpets/gui/PetMenus.java b/src/main/java/net/tfminecraft/companionpets/gui/PetMenus.java
index e3621a6..5306ac3 100644
--- a/src/main/java/net/tfminecraft/companionpets/gui/PetMenus.java
+++ b/src/main/java/net/tfminecraft/companionpets/gui/PetMenus.java
@@ -77,7 +77,7 @@ public void openCare(org.bukkit.entity.Player player, Pet pet, boolean petHouseB
     }
 
     public void refreshCare(org.bukkit.entity.Player player, Pet pet) {
-        if (!(player.getOpenInventory().getTopInventory().getHolder() instanceof MenuHolder holder)
+        if (!(player.getOpenInventory().getTopInventory().getHolder(false) instanceof MenuHolder holder)
                 || holder.kind() != MenuHolder.Kind.CARE
                 || !pet.id().equals(holder.petId())) {
             return;
@@ -87,7 +87,7 @@ public void refreshCare(org.bukkit.entity.Player player, Pet pet) {
 
     private void fillCare(org.bukkit.entity.Player player, Inventory inventory, Pet pet) {
         fillProfile(inventory, pet, runtime.owns(pet, player),
-                inventory.getHolder() instanceof MenuHolder holder && holder.petHouseBack());
+                inventory.getHolder(false) instanceof MenuHolder holder && holder.petHouseBack());
     }
 
     public void fillInformation(Inventory inventory, Pet pet) {
@@ -334,7 +334,7 @@ public void openTricks(org.bukkit.entity.Player player, Pet pet, String word, in
 
     private void inheritPetHouseNavigation(org.bukkit.entity.Player player, MenuHolder holder) {
         Inventory previousInventory = player.getOpenInventory().getTopInventory();
-        if (previousInventory != null && previousInventory.getHolder() instanceof MenuHolder previous
+        if (previousInventory != null && previousInventory.getHolder(false) instanceof MenuHolder previous
                 && holder.petId().equals(previous.petId())) {
             holder.petHouseBack(previous.petHouseBack());
             holder.petHousePage(previous.petHousePage());
diff --git a/src/main/java/net/tfminecraft/companionpets/listen/PetListener.java b/src/main/java/net/tfminecraft/companionpets/listen/PetListener.java
index 50d43f6..592fe4c 100644
--- a/src/main/java/net/tfminecraft/companionpets/listen/PetListener.java
+++ b/src/main/java/net/tfminecraft/companionpets/listen/PetListener.java
@@ -138,7 +138,7 @@ public void onChat(AsyncPlayerChatEvent event) {
 
     @EventHandler
     public void onClick(InventoryClickEvent event) {
-        InventoryHolder holder = event.getView().getTopInventory().getHolder();
+        InventoryHolder holder = event.getView().getTopInventory().getHolder(false);
         if (!(holder instanceof MenuHolder menu) || !(event.getWhoClicked() instanceof Player player)) {
             return;
         }
@@ -152,14 +152,14 @@ public void onClick(InventoryClickEvent event) {
 
     @EventHandler
     public void onDrag(InventoryDragEvent event) {
-        if (event.getView().getTopInventory().getHolder() instanceof MenuHolder) {
+        if (event.getView().getTopInventory().getHolder(false) instanceof MenuHolder) {
             event.setCancelled(true);
         }
     }
 
     @EventHandler
     public void onClose(InventoryCloseEvent event) {
-        if (event.getInventory().getHolder() instanceof MenuHolder menu
+        if (event.getInventory().getHolder(false) instanceof MenuHolder menu
                 && menu.kind() == MenuHolder.Kind.TRICK
                 && !menu.navigating()
                 && event.getPlayer() instanceof Player player) {
diff --git a/src/main/java/net/tfminecraft/companionpets/ownership/CharacterLifecycle.java b/src/main/java/net/tfminecraft/companionpets/ownership/CharacterLifecycle.java
index 007b619..1358314 100644
--- a/src/main/java/net/tfminecraft/companionpets/ownership/CharacterLifecycle.java
+++ b/src/main/java/net/tfminecraft/companionpets/ownership/CharacterLifecycle.java
@@ -20,7 +20,7 @@ public void end(CharacterSessionEndEvent event) {
         Player player = Bukkit.getPlayer(event.getSession().ref().ownerId());
         if (player != null) {
             actions.ownerSessionChanged(player);
-            if (player.getOpenInventory().getTopInventory().getHolder() instanceof MenuHolder) player.closeInventory();
+            if (player.getOpenInventory().getTopInventory().getHolder(false) instanceof MenuHolder) player.closeInventory();
         }
         runtime.sessions().clearPlayer(event.getSession().ref().ownerId());
     }
diff --git a/src/main/java/net/tfminecraft/companionpets/staff/StaffMenus.java b/src/main/java/net/tfminecraft/companionpets/staff/StaffMenus.java
index c554d2b..ae3ac34 100644
--- a/src/main/java/net/tfminecraft/companionpets/staff/StaffMenus.java
+++ b/src/main/java/net/tfminecraft/companionpets/staff/StaffMenus.java
@@ -101,7 +101,7 @@ private static ItemStack named(ItemStack source, String title, String... lore) {
     }
 
     @EventHandler public void onClick(InventoryClickEvent event) {
-        if (!(event.getView().getTopInventory().getHolder() instanceof StaffMenuHolder holder)) return;
+        if (!(event.getView().getTopInventory().getHolder(false) instanceof StaffMenuHolder holder)) return;
         event.setCancelled(true);
         if (!(event.getWhoClicked() instanceof Player player) || !holder.viewer().equals(player.getUniqueId())) return;
         if (event.getClickedInventory() != event.getView().getTopInventory() || !(event.getClick().isLeftClick() || event.getClick().isRightClick())
@@ -109,6 +109,6 @@ private static ItemStack named(ItemStack source, String title, String... lore) {
         if (allowed(player, "list")) holder.click(event.getSlot(), event.getClick().isRightClick());
     }
     @EventHandler public void onDrag(InventoryDragEvent event) {
-        if (event.getView().getTopInventory().getHolder() instanceof StaffMenuHolder) event.setCancelled(true);
+        if (event.getView().getTopInventory().getHolder(false) instanceof StaffMenuHolder) event.setCancelled(true);
     }
 }
diff --git a/src/test/java/net/tfminecraft/companionpets/testutil/HolderLookupPatch.java b/src/test/java/net/tfminecraft/companionpets/testutil/HolderLookupPatch.java
new file mode 100644
index 0000000..52367a9
--- /dev/null
+++ b/src/test/java/net/tfminecraft/companionpets/testutil/HolderLookupPatch.java
@@ -0,0 +1,91 @@
+package net.tfminecraft.companionpets.testutil;
+
+import static net.bytebuddy.matcher.ElementMatchers.is;
+import static net.bytebuddy.matcher.ElementMatchers.named;
+import static net.bytebuddy.matcher.ElementMatchers.takesArguments;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import net.bytebuddy.agent.ByteBuddyAgent;
+import net.bytebuddy.agent.builder.AgentBuilder;
+import net.bytebuddy.asm.Advice;
+import net.bytebuddy.description.type.TypeDescription;
+import net.bytebuddy.dynamic.DynamicType;
+import net.bytebuddy.utility.JavaModule;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryHolder;
+import org.junit.platform.launcher.LauncherSession;
+import org.junit.platform.launcher.LauncherSessionListener;
+import org.mockbukkit.mockbukkit.inventory.InventoryMock;
+
+/**
+ * MockBukkit throws on Paper's {@code getHolder(false)}. Its inventories hold no block snapshot,
+ * so the patch answers with the plain holder, which is what Paper returns for plugin GUIs.
+ */
+public final class HolderLookupPatch implements LauncherSessionListener {
+    private static boolean installed;
+
+    @Override
+    public void launcherSessionOpened(LauncherSession session) {
+        install();
+    }
+
+    /** Patches {@link InventoryMock#getHolder(boolean)} once per test JVM. */
+    public static synchronized void install() {
+        if (installed) {
+            return;
+        }
+        AtomicBoolean patched = new AtomicBoolean();
+        AtomicBoolean rejected = new AtomicBoolean();
+        new AgentBuilder.Default()
+                .disableClassFormatChanges()
+                .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
+                .with(AgentBuilder.InitializationStrategy.NoOp.INSTANCE)
+                .with(AgentBuilder.TypeStrategy.Default.REDEFINE)
+                .with(AgentBuilder.Listener.StreamWriting.toSystemError().withErrorsOnly())
+                .with(new AgentBuilder.Listener.Adapter() {
+                    @Override
+                    public void onTransformation(TypeDescription type, ClassLoader loader, JavaModule module,
+                            boolean loaded, DynamicType dynamicType) {
+                        if (type.getName().equals(InventoryMock.class.getName())) {
+                            patched.set(true);
+                        }
+                    }
+
+                    // The JVM can still reject the new bytes after onTransformation.
+                    @Override
+                    public void onError(String typeName, ClassLoader loader, JavaModule module, boolean loaded,
+                            Throwable throwable) {
+                        if (typeName.equals(InventoryMock.class.getName())) {
+                            rejected.set(true);
+                        }
+                    }
+                })
+                .type(is(InventoryMock.class))
+                .transform((builder, type, loader, module, domain) -> builder.visit(Advice.to(PlainHolder.class)
+                        .on(named("getHolder").and(takesArguments(boolean.class)))))
+                .installOn(ByteBuddyAgent.install());
+        // A failed retransformation only reaches the listeners, so check it took before marking it done.
+        if (!patched.get() || rejected.get()) {
+            throw new IllegalStateException("Could not patch InventoryMock#getHolder(boolean)");
+        }
+        installed = true;
+    }
+
+    /** Skips the throwing body and returns {@code getHolder()} instead. */
+    static final class PlainHolder {
+        private PlainHolder() {
+        }
+
+        @Advice.OnMethodEnter(skipOn = Advice.OnNonDefaultValue.class)
+        static boolean skip() {
+            return true;
+        }
+
+        @Advice.OnMethodExit
+        static void exit(@Advice.This Inventory inventory,
+                @Advice.Return(readOnly = false) InventoryHolder holder) {
+            holder = inventory.getHolder();
+        }
+    }
+}
diff --git a/src/test/resources/META-INF/services/org.junit.platform.launcher.LauncherSessionListener b/src/test/resources/META-INF/services/org.junit.platform.launcher.LauncherSessionListener
new file mode 100644
index 0000000..390a242
--- /dev/null
+++ b/src/test/resources/META-INF/services/org.junit.platform.launcher.LauncherSessionListener
@@ -0,0 +1 @@
+net.tfminecraft.companionpets.testutil.HolderLookupPatch