diff --git a/pom.xml b/pom.xml
index 3334243..2bde20c 100644
--- a/pom.xml
+++ b/pom.xml
@@ -67,6 +67,12 @@
             <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>
@@ -113,7 +119,7 @@
                 <artifactId>maven-surefire-plugin</artifactId>
                 <version>3.5.4</version>
                 <configuration>
-                    <argLine>@{argLine} -javaagent:${org.mockito:mockito-core:jar} -Xshare:off</argLine>
+                    <argLine>@{argLine} -javaagent:${org.mockito:mockito-core:jar} -javaagent:${net.bytebuddy:byte-buddy-agent:jar} -Xshare:off</argLine>
                     <failIfNoTests>true</failIfNoTests>
                 </configuration>
             </plugin>
diff --git a/src/main/java/net/tfminecraft/surgery/SurgeryPlugin.java b/src/main/java/net/tfminecraft/surgery/SurgeryPlugin.java
index 76aeef4..c0bbaf5 100644
--- a/src/main/java/net/tfminecraft/surgery/SurgeryPlugin.java
+++ b/src/main/java/net/tfminecraft/surgery/SurgeryPlugin.java
@@ -72,7 +72,7 @@ public void onDisable() {
         // a new classloader, so the instanceof check in the listener no longer
         // matches and players could pull items out of stale menus
         for (Player player : getServer().getOnlinePlayers()) {
-            if (player.getOpenInventory().getTopInventory().getHolder() instanceof SurgeryMenuHolder) {
+            if (player.getOpenInventory().getTopInventory().getHolder(false) instanceof SurgeryMenuHolder) {
                 player.closeInventory();
             }
         }
diff --git a/src/main/java/net/tfminecraft/surgery/managers/SurgeryCompletionHandler.java b/src/main/java/net/tfminecraft/surgery/managers/SurgeryCompletionHandler.java
index 2e9ef20..1f341be 100644
--- a/src/main/java/net/tfminecraft/surgery/managers/SurgeryCompletionHandler.java
+++ b/src/main/java/net/tfminecraft/surgery/managers/SurgeryCompletionHandler.java
@@ -191,7 +191,7 @@ private void reportFailure(Player surgeon, String message, String extra) {
 
     private Inventory surgeryMenu(Player surgeon, Outcome outcome) {
         Inventory menu = surgeon.getOpenInventory().getTopInventory();
-        return menu.getHolder() instanceof SurgeryMenuHolder holder && holder.matches(surgeon, outcome.operationId())
+        return menu.getHolder(false) instanceof SurgeryMenuHolder holder && holder.matches(surgeon, outcome.operationId())
                 ? menu : null;
     }
 
diff --git a/src/main/java/net/tfminecraft/surgery/managers/SurgeryMenuManager.java b/src/main/java/net/tfminecraft/surgery/managers/SurgeryMenuManager.java
index 9c641f1..75e7c30 100644
--- a/src/main/java/net/tfminecraft/surgery/managers/SurgeryMenuManager.java
+++ b/src/main/java/net/tfminecraft/surgery/managers/SurgeryMenuManager.java
@@ -89,7 +89,7 @@ public void openSurgeryMenu(Player surgeon, Player patient, HealingInjury ailmen
     // Checks if an inventory is the surgery menu (by holder, not title)
     // ==============================================
     public boolean isSurgeryMenu(org.bukkit.inventory.Inventory inventory) {
-        return inventory != null && inventory.getHolder() instanceof SurgeryMenuHolder;
+        return inventory != null && inventory.getHolder(false) instanceof SurgeryMenuHolder;
     }
 
     // ==============================================
@@ -103,7 +103,7 @@ public void handleItemClick(Player player, Inventory inventory, ItemStack clicke
     }
 
     private boolean ownsMenu(Player player, Inventory inventory) {
-        return inventory.getHolder() instanceof SurgeryMenuHolder holder
+        return inventory.getHolder(false) instanceof SurgeryMenuHolder holder
                 && holder.matches(player, stateManager.getOperationId(player.getUniqueId()));
     }
 
diff --git a/src/test/java/net/tfminecraft/surgery/HolderLookupPatch.java b/src/test/java/net/tfminecraft/surgery/HolderLookupPatch.java
new file mode 100644
index 0000000..a6294e6
--- /dev/null
+++ b/src/test/java/net/tfminecraft/surgery/HolderLookupPatch.java
@@ -0,0 +1,91 @@
+package net.tfminecraft.surgery;
+
+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..bd70596
--- /dev/null
+++ b/src/test/resources/META-INF/services/org.junit.platform.launcher.LauncherSessionListener
@@ -0,0 +1 @@
+net.tfminecraft.surgery.HolderLookupPatch