diff --git a/src/main/java/minevalley/chestluck/api/core/Lockable.java b/src/main/java/minevalley/chestluck/api/core/Lockable.java
index a4d5958..e92ee69 100644
--- a/src/main/java/minevalley/chestluck/api/core/Lockable.java
+++ b/src/main/java/minevalley/chestluck/api/core/Lockable.java
@@ -1,5 +1,6 @@
 package minevalley.chestluck.api.core;
 
+import minevalley.chestluck.api.core.capabilities.Capability;
 import minevalley.core.api.Registrant;
 import org.bukkit.Location;
 import org.jetbrains.annotations.Contract;
@@ -90,7 +91,7 @@ public interface Lockable {
      */
     @Nonnull
     @Contract(pure = true)
-    default <T> Optional<T> as(@Nonnull Class<T> capability) throws IllegalArgumentException {
+    default <T extends Capability> Optional<T> as(@Nonnull Class<T> capability) throws IllegalArgumentException {
         if (capability == null) throw new IllegalArgumentException("Capability class cannot be null");
         return capability.isInstance(this) ? Optional.of(capability.cast(this)) : Optional.empty();
     }
diff --git a/src/main/java/minevalley/chestluck/api/core/capabilities/AutoCloseable.java b/src/main/java/minevalley/chestluck/api/core/capabilities/AutoCloseable.java
index 59e0232..50e611f 100644
--- a/src/main/java/minevalley/chestluck/api/core/capabilities/AutoCloseable.java
+++ b/src/main/java/minevalley/chestluck/api/core/capabilities/AutoCloseable.java
@@ -6,7 +6,7 @@
 import javax.annotation.Nonnull;
 
 @SuppressWarnings("unused")
-public interface AutoCloseable {
+public interface AutoCloseable extends Capability{
 
     /**
      * Checks whether the AutoCloseable should automatically close after it has been opened
diff --git a/src/main/java/minevalley/chestluck/api/core/capabilities/AutoOpenable.java b/src/main/java/minevalley/chestluck/api/core/capabilities/AutoOpenable.java
index 7f50d4b..d21bbb6 100644
--- a/src/main/java/minevalley/chestluck/api/core/capabilities/AutoOpenable.java
+++ b/src/main/java/minevalley/chestluck/api/core/capabilities/AutoOpenable.java
@@ -6,7 +6,7 @@
 import javax.annotation.Nonnull;
 
 @SuppressWarnings("unused")
-public interface AutoOpenable {
+public interface AutoOpenable extends Capability {
 
     /**
      * Checks whether the AutoOpenable will automatically open for registrants.
diff --git a/src/main/java/minevalley/chestluck/api/core/capabilities/Capability.java b/src/main/java/minevalley/chestluck/api/core/capabilities/Capability.java
new file mode 100644
index 0000000..6421bdf
--- /dev/null
+++ b/src/main/java/minevalley/chestluck/api/core/capabilities/Capability.java
@@ -0,0 +1,6 @@
+package minevalley.chestluck.api.core.capabilities;
+
+@SuppressWarnings("unused")
+public interface Capability {
+
+}
\ No newline at end of file
diff --git a/src/main/java/minevalley/chestluck/api/core/capabilities/ItemReceiver.java b/src/main/java/minevalley/chestluck/api/core/capabilities/ItemReceiver.java
index 3f93194..7ff3e9f 100644
--- a/src/main/java/minevalley/chestluck/api/core/capabilities/ItemReceiver.java
+++ b/src/main/java/minevalley/chestluck/api/core/capabilities/ItemReceiver.java
@@ -6,7 +6,7 @@
 import javax.annotation.Nonnull;
 
 @SuppressWarnings("unused")
-public interface ItemReceiver {
+public interface ItemReceiver extends Capability {
 
     /**
      * Checks whether the ItemReceiver can receive items or not.
diff --git a/src/main/java/minevalley/chestluck/api/core/capabilities/ItemSupplier.java b/src/main/java/minevalley/chestluck/api/core/capabilities/ItemSupplier.java
index 5b2b590..8c2d769 100644
--- a/src/main/java/minevalley/chestluck/api/core/capabilities/ItemSupplier.java
+++ b/src/main/java/minevalley/chestluck/api/core/capabilities/ItemSupplier.java
@@ -6,7 +6,7 @@
 import javax.annotation.Nonnull;
 
 @SuppressWarnings("unused")
-public interface ItemSupplier {
+public interface ItemSupplier extends Capability {
 
     /**
      * Checks whether the ItemReceiver can supply items or not.