diff --git a/build.gradle b/build.gradle
index 9220e3c..a959130 100644
--- a/build.gradle
+++ b/build.gradle
@@ -6,7 +6,7 @@ plugins {
 
 subprojects {
     group = 'dev.tommyjs'
-    version = '2.5.1'
+    version = '2.5.2'
 
     apply plugin: 'java-library'
     apply plugin: 'com.github.johnrengelman.shadow'
@@ -63,8 +63,8 @@ subprojects {
     }
 
     java {
-        sourceCompatibility = JavaVersion.VERSION_23
-        targetCompatibility = JavaVersion.VERSION_23
+        sourceCompatibility = JavaVersion.VERSION_21
+        targetCompatibility = JavaVersion.VERSION_21
         withSourcesJar()
     }
 }
\ No newline at end of file
diff --git a/futur-api/src/main/java/dev/tommyjs/futur/function/FunctionAdapter.java b/futur-api/src/main/java/dev/tommyjs/futur/function/FunctionAdapter.java
index fcbc009..70d545a 100644
--- a/futur-api/src/main/java/dev/tommyjs/futur/function/FunctionAdapter.java
+++ b/futur-api/src/main/java/dev/tommyjs/futur/function/FunctionAdapter.java
@@ -12,14 +12,14 @@ public final class FunctionAdapter {
     }
 
     public static <K, V> @NotNull ExceptionalFunction<K, V> adapt(@NotNull ExceptionalRunnable runnable) {
-        return _ -> {
+        return v -> {
             runnable.run();
             return null;
         };
     }
 
     public static <K, T> @NotNull ExceptionalFunction<K, T> adapt(@NotNull ExceptionalSupplier<T> supplier) {
-        return _ -> supplier.get();
+        return v -> supplier.get();
     }
 
 }
diff --git a/futur-api/src/main/java/dev/tommyjs/futur/promise/AbstractPromise.java b/futur-api/src/main/java/dev/tommyjs/futur/promise/AbstractPromise.java
index a4f8942..bb5c6a6 100644
--- a/futur-api/src/main/java/dev/tommyjs/futur/promise/AbstractPromise.java
+++ b/futur-api/src/main/java/dev/tommyjs/futur/promise/AbstractPromise.java
@@ -139,7 +139,7 @@ public abstract class AbstractPromise<T> implements Promise<T> {
 
     @Override
     public @NotNull Promise<Void> thenRun(@NotNull ExceptionalRunnable task) {
-        return thenApply(_ -> {
+        return thenApply(v -> {
             task.run();
             return null;
         });
@@ -155,7 +155,7 @@ public abstract class AbstractPromise<T> implements Promise<T> {
 
     @Override
     public <V> @NotNull Promise<V> thenSupply(@NotNull ExceptionalSupplier<V> task) {
-        return thenApply(_ -> task.get());
+        return thenApply(v -> task.get());
     }
 
     @Override
@@ -228,13 +228,13 @@ public abstract class AbstractPromise<T> implements Promise<T> {
     private <F> void execute(@NotNull Promise<?> promise, @NotNull Runnable task, @NotNull PromiseExecutor<F> executor)
         throws Exception {
         F future = executor.run(task);
-        promise.addDirectListener(_ -> executor.cancel(future));
+        promise.addDirectListener(v -> executor.cancel(future));
     }
 
     private <F> void schedule(@NotNull Promise<?> promise, @NotNull Runnable task, long delay, @NotNull TimeUnit unit,
                               @NotNull PromiseScheduler<F> scheduler) throws Exception {
         F future = scheduler.schedule(task, delay, unit);
-        promise.addDirectListener(_ -> scheduler.cancel(future));
+        promise.addDirectListener(v -> scheduler.cancel(future));
     }
 
     private <V> @NotNull Promise<V> thenCompose(@NotNull ExceptionalFunction<T, Promise<V>> task,
@@ -494,12 +494,12 @@ public abstract class AbstractPromise<T> implements Promise<T> {
 
     @Override
     public @NotNull Promise<T> orDefault(@Nullable T defaultValue) {
-        return orDefault(_ -> defaultValue);
+        return orDefault(v -> defaultValue);
     }
 
     @Override
     public @NotNull Promise<T> orDefault(@NotNull ExceptionalSupplier<T> supplier) {
-        return orDefault(_ -> supplier.get());
+        return orDefault(v -> supplier.get());
     }
 
     @Override
diff --git a/futur-api/src/main/java/dev/tommyjs/futur/promise/AbstractPromiseFactory.java b/futur-api/src/main/java/dev/tommyjs/futur/promise/AbstractPromiseFactory.java
index c38af99..91688fb 100644
--- a/futur-api/src/main/java/dev/tommyjs/futur/promise/AbstractPromiseFactory.java
+++ b/futur-api/src/main/java/dev/tommyjs/futur/promise/AbstractPromiseFactory.java
@@ -40,7 +40,7 @@ public abstract class AbstractPromiseFactory implements PromiseFactory {
         });
 
         if (future != null) {
-            promise.onCancel(_ -> future.cancel(true));
+            promise.onCancel(v -> future.cancel(true));
         }
 
         return promise;
@@ -48,7 +48,7 @@ public abstract class AbstractPromiseFactory implements PromiseFactory {
 
     @Override
     public <K, V> @NotNull Promise<Map.Entry<K, V>> combine(@NotNull Promise<K> p1, @NotNull Promise<V> p2) {
-        return all(p1, p2).thenApply(_ -> new AbstractMap.SimpleImmutableEntry<>(
+        return all(p1, p2).thenApply(v -> new AbstractMap.SimpleImmutableEntry<>(
             Objects.requireNonNull(p1.getCompletion()).getResult(),
             Objects.requireNonNull(p2.getCompletion()).getResult()
         ));
diff --git a/futur-api/src/main/java/dev/tommyjs/futur/promise/BasePromise.java b/futur-api/src/main/java/dev/tommyjs/futur/promise/BasePromise.java
index c607534..8560d7f 100644
--- a/futur-api/src/main/java/dev/tommyjs/futur/promise/BasePromise.java
+++ b/futur-api/src/main/java/dev/tommyjs/futur/promise/BasePromise.java
@@ -55,7 +55,7 @@ public abstract class BasePromise<T> extends AbstractPromise<T> implements Compl
                                                           PromiseScheduler<F> scheduler) {
         runCompleter(this, () -> {
             F future = scheduler.schedule(() -> completeExceptionally(e), delay, unit);
-            addDirectListener(_ -> scheduler.cancel(future));
+            addDirectListener(v -> scheduler.cancel(future));
         });
 
         return this;
diff --git a/futur-api/src/main/java/dev/tommyjs/futur/util/PromiseUtil.java b/futur-api/src/main/java/dev/tommyjs/futur/util/PromiseUtil.java
index f2a87bd..662e0f0 100644
--- a/futur-api/src/main/java/dev/tommyjs/futur/util/PromiseUtil.java
+++ b/futur-api/src/main/java/dev/tommyjs/futur/util/PromiseUtil.java
@@ -35,7 +35,7 @@ public class PromiseUtil {
      * @param to   the promise to cancel upon completion
      */
     public static void cancelOnComplete(@NotNull Promise<?> from, @NotNull Promise<?> to) {
-        from.addDirectListener(_ -> to.cancel());
+        from.addDirectListener(v -> to.cancel());
     }
 
     /**
diff --git a/futur-api/src/test/java/dev/tommyjs/futur/PromiseTests.java b/futur-api/src/test/java/dev/tommyjs/futur/PromiseTests.java
index ce99c46..7d89a17 100644
--- a/futur-api/src/test/java/dev/tommyjs/futur/PromiseTests.java
+++ b/futur-api/src/test/java/dev/tommyjs/futur/PromiseTests.java
@@ -263,7 +263,7 @@ public final class PromiseTests {
     @Test
     public void testImmediate2() {
         var resolved = promises.resolve(10);
-        var promise = promises.start().thenCompose(_ -> resolved);
+        var promise = promises.start().thenCompose(v -> resolved);
         assert promise.isCompleted() && promise instanceof CompletedPromise;
     }