diff --git a/src/main/java/net/theevilreaper/aves/inventory/BaseInventoryBuilderImpl.java b/src/main/java/net/theevilreaper/aves/inventory/BaseInventoryBuilderImpl.java
index 2bbb9309..56fcf3cf 100644
--- a/src/main/java/net/theevilreaper/aves/inventory/BaseInventoryBuilderImpl.java
+++ b/src/main/java/net/theevilreaper/aves/inventory/BaseInventoryBuilderImpl.java
@@ -42,11 +42,11 @@ protected BaseInventoryBuilderImpl(@NotNull InventoryType type) {
     @Override
     public void register() {
         this.checkListenerState(this.openListener, this.closeListener, this.clickListener);
-        if (this.openFunction == null) {
+        if (this.openFunction != null) {
             this.openListener = registerOpen(this, holder);
         }
 
-        if (this.closeFunction == null) {
+        if (this.closeFunction != null) {
             this.closeListener = registerClose(this, holder);
         }
 
diff --git a/src/test/java/net/theevilreaper/aves/inventory/BaseInventoryBuilderImplIntegrationTest.java b/src/test/java/net/theevilreaper/aves/inventory/BaseInventoryBuilderImplIntegrationTest.java
new file mode 100644
index 00000000..8d10bbce
--- /dev/null
+++ b/src/test/java/net/theevilreaper/aves/inventory/BaseInventoryBuilderImplIntegrationTest.java
@@ -0,0 +1,130 @@
+package net.theevilreaper.aves.inventory;
+
+import net.kyori.adventure.text.Component;
+import net.kyori.adventure.text.serializer.plain.PlainTextComponentSerializer;
+import net.minestom.server.entity.Player;
+import net.minestom.server.event.EventFilter;
+import net.minestom.server.event.inventory.InventoryCloseEvent;
+import net.minestom.server.event.inventory.InventoryOpenEvent;
+import net.minestom.server.instance.Instance;
+import net.minestom.server.inventory.InventoryType;
+import net.minestom.server.network.packet.server.play.SystemChatPacket;
+import net.minestom.testing.Collector;
+import net.minestom.testing.Env;
+import net.minestom.testing.TestConnection;
+import net.minestom.testing.extension.MicrotusExtension;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+@ExtendWith(MicrotusExtension.class)
+class BaseInventoryBuilderImplIntegrationTest {
+
+    private static final Component TITLE_COMPONENT = Component.text("Test");
+
+    private Instance instance;
+    private TestConnection testConnection;
+    private Player player;
+
+    @BeforeEach
+    void setup(Env env) {
+        instance = env.createFlatInstance();
+        testConnection = env.createConnection();
+        player = testConnection.connect(instance);
+    }
+
+    @AfterEach
+    void teardown(Env env) {
+        env.destroyInstance(instance, true);
+    }
+
+    @Test
+    void testCloseFunctionCall(Env env) {
+        GlobalInventoryBuilder testInventory = buildInventory();
+        testInventory.setCloseFunction(event ->
+                event.getPlayer().sendMessage(Component.text("Closed"))
+        );
+        testInventory.register();
+
+        assertNotNull(testInventory.getInventory());
+
+        player.openInventory(testInventory.getInventory());
+        assertNotNull(player.getOpenInventory());
+        assertInstanceOf(CustomInventory.class, player.getOpenInventory());
+
+        Collector<SystemChatPacket> chatCollector = testConnection.trackIncoming(SystemChatPacket.class);
+        Collector<InventoryCloseEvent> closeTracker = env.trackEvent(InventoryCloseEvent.class, EventFilter.INVENTORY, testInventory.getInventory());
+
+        player.closeInventory();
+
+        closeTracker.assertSingle(event -> {
+            assertInstanceOf(CustomInventory.class, event.getInventory());
+            CustomInventory inventory = (CustomInventory) event.getInventory();
+            assertEquals("Test", PlainTextComponentSerializer.plainText().serialize(inventory.getTitle()));
+        });
+
+        env.tick();
+        assertSingleChatMessage(chatCollector, "Closed");
+    }
+
+    @Test
+    void testOpenFunctionCall(Env env) {
+        GlobalInventoryBuilder testInventory = buildInventory();
+        testInventory.setOpenFunction(event ->
+                event.getPlayer().sendMessage(Component.text("Opened"))
+        );
+        testInventory.register();
+
+        assertNotNull(testInventory.getInventory());
+
+        Collector<SystemChatPacket> chatCollector = testConnection.trackIncoming(SystemChatPacket.class);
+        Collector<InventoryOpenEvent> openTracker = env.trackEvent(InventoryOpenEvent.class, EventFilter.INVENTORY, testInventory.getInventory());
+
+        player.openInventory(testInventory.getInventory());
+        assertNotNull(player.getOpenInventory());
+        assertInstanceOf(CustomInventory.class, player.getOpenInventory());
+
+        openTracker.assertSingle(event -> {
+            assertInstanceOf(CustomInventory.class, event.getInventory());
+            CustomInventory inventory = (CustomInventory) event.getInventory();
+            assertEquals("Test", PlainTextComponentSerializer.plainText().serialize(inventory.getTitle()));
+        });
+
+        env.tick();
+        assertSingleChatMessage(chatCollector, "Opened");
+    }
+
+    /**
+     * Creates a pre-configured {@link GlobalInventoryBuilder} with {@link #TITLE_COMPONENT}
+     * as title and {@link InventoryType#ANVIL} as type, including a matching layout.
+     *
+     * @return a new {@link GlobalInventoryBuilder} ready for use in tests
+     */
+    private GlobalInventoryBuilder buildInventory() {
+        GlobalInventoryBuilder builder = new GlobalInventoryBuilder(TITLE_COMPONENT, InventoryType.ANVIL);
+        builder.setLayout(InventoryLayout.fromType(builder.getType()));
+        return builder;
+    }
+
+    /**
+     * Asserts that the given {@link Collector} contains exactly one {@link SystemChatPacket}
+     * whose first component matches the expected plain-text message.
+     *
+     * @param collector the packet collector to assert against
+     * @param expected  the expected plain-text message
+     */
+    private void assertSingleChatMessage(Collector<SystemChatPacket> collector, String expected) {
+        collector.assertSingle(packet -> {
+            assertNotNull(packet.components());
+            assertEquals(1, packet.components().size());
+            Component first = packet.components().iterator().next();
+            assertNotNull(first);
+            assertEquals(expected, PlainTextComponentSerializer.plainText().serialize(first));
+        });
+    }
+}
\ No newline at end of file