diff --git a/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/Publisher.java b/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/Publisher.java
index c1f457a81fe0..51d1cf5d4ed7 100644
--- a/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/Publisher.java
+++ b/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/Publisher.java
@@ -99,7 +99,7 @@ public class Publisher {
   private final PublisherStub publisherStub;
 
   private final ScheduledExecutorService executor;
-  private final SequentialExecutorService<PublishResponse> sequentialExecutor;
+  private final SequentialExecutorService sequentialExecutor;
   private final AtomicBoolean shutdown;
   private final List<AutoCloseable> closeables;
   private final MessageWaiter messagesWaiter;
@@ -127,7 +127,7 @@ private Publisher(Builder builder) throws IOException {
     messagesBatchLock = new ReentrantLock();
     activeAlarm = new AtomicBoolean(false);
     executor = builder.executorProvider.getExecutor();
-    sequentialExecutor = new SequentialExecutorService<>(executor);
+    sequentialExecutor = new SequentialExecutorService(executor);
     if (builder.executorProvider.shouldAutoClose()) {
       closeables =
           Collections.<AutoCloseable>singletonList(new ExecutorAsBackgroundResource(executor));
@@ -398,9 +398,9 @@ public void run() {
       executor.execute(task);
     } else {
       // If ordering key is specified, publish the batch using the sequential executor.
-      Callable<ApiFuture> func =
-          new Callable<ApiFuture>() {
-            public ApiFuture call() {
+      Callable<ApiFuture<PublishResponse>> func =
+          new Callable<ApiFuture<PublishResponse>>() {
+            public ApiFuture<PublishResponse> call() {
               return publishCall(outstandingBatch);
             }
           };
diff --git a/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/SequentialExecutorService.java b/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/SequentialExecutorService.java
index bbebd8db4de2..bbc3b2e74d67 100644
--- a/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/SequentialExecutorService.java
+++ b/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/SequentialExecutorService.java
@@ -41,7 +41,7 @@ interface CancellableRunnable extends Runnable {
  * key will be run only when its predecessor has been completed while tasks with different keys can
  * be run in parallel.
  */
-final class SequentialExecutorService<T> {
+final class SequentialExecutorService {
   private static final Logger logger = Logger.getLogger(SequentialExecutorService.class.getName());
 
   private final CallbackExecutor callbackExecutor;
@@ -56,7 +56,7 @@ final class SequentialExecutorService<T> {
    * Runs asynchronous {@code Callable} tasks sequentially. If one of the tasks fails, other tasks
    * with the same key that have not been executed will be cancelled.
    */
-  ApiFuture<T> submit(final String key, final Callable<ApiFuture> callable) {
+  <T> ApiFuture<T> submit(final String key, final Callable<ApiFuture<T>> callable) {
     return callbackExecutor.submit(key, callable);
   }
 
@@ -146,7 +146,7 @@ private static class CallbackExecutor extends SequentialExecutor {
       super(executor);
     }
 
-    <T> ApiFuture<T> submit(final String key, final Callable<ApiFuture> callable) {
+    <T> ApiFuture<T> submit(final String key, final Callable<ApiFuture<T>> callable) {
       final SettableApiFuture<T> future = SettableApiFuture.create();
       execute(
           key,
diff --git a/google-cloud-clients/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/SequentialExecutorServiceTest.java b/google-cloud-clients/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/SequentialExecutorServiceTest.java
index b592194b410a..00ea85533e06 100644
--- a/google-cloud-clients/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/SequentialExecutorServiceTest.java
+++ b/google-cloud-clients/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/SequentialExecutorServiceTest.java
@@ -46,9 +46,9 @@ public final class SequentialExecutorServiceTest {
           .setExecutorThreadCount(5 * Runtime.getRuntime().availableProcessors())
           .build();
 
-  static class AsyncTaskCallable implements Callable<ApiFuture> {
+  static class AsyncTaskCallable implements Callable<ApiFuture<String>> {
     boolean isCalled = false;
-    SettableApiFuture<String> result = SettableApiFuture.<String>create();
+    SettableApiFuture<String> result = SettableApiFuture.create();
 
     @Override
     public ApiFuture<String> call() {
@@ -71,8 +71,8 @@ public void finish() {
 
   @Test
   public void testExecutorRunsNextTaskWhenPrevResponseReceived() throws Exception {
-    SequentialExecutorService<String> sequentialExecutorService =
-        new SequentialExecutorService<>(executorProvider.getExecutor());
+    SequentialExecutorService sequentialExecutorService =
+        new SequentialExecutorService(executorProvider.getExecutor());
     AsyncTaskCallable callable1 = new AsyncTaskCallable();
     AsyncTaskCallable callable2 = new AsyncTaskCallable();
     AsyncTaskCallable callable3 = new AsyncTaskCallable();
@@ -97,8 +97,8 @@ public void testExecutorRunsNextTaskWhenPrevResponseReceived() throws Exception
 
   @Test
   public void testExecutorRunsDifferentKeySimultaneously() throws Exception {
-    SequentialExecutorService<String> sequentialExecutorService =
-        new SequentialExecutorService<>(executorProvider.getExecutor());
+    SequentialExecutorService sequentialExecutorService =
+        new SequentialExecutorService(executorProvider.getExecutor());
     AsyncTaskCallable callable1 = new AsyncTaskCallable();
     AsyncTaskCallable callable2 = new AsyncTaskCallable();
     AsyncTaskCallable callable3 = new AsyncTaskCallable();
@@ -126,8 +126,8 @@ public void testExecutorRunsDifferentKeySimultaneously() throws Exception {
 
   @Test
   public void testExecutorCancelsAllTasksWhenOneFailed() throws Exception {
-    SequentialExecutorService<String> sequentialExecutorService =
-        new SequentialExecutorService<>(executorProvider.getExecutor());
+    SequentialExecutorService sequentialExecutorService =
+        new SequentialExecutorService(executorProvider.getExecutor());
     AsyncTaskCallable callable1 = new AsyncTaskCallable();
     AsyncTaskCallable callable2 = new AsyncTaskCallable();
     AsyncTaskCallable callable3 = new AsyncTaskCallable();