diff --git a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/internal/RequestDataSupplierAdapter.java b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/internal/RequestDataSupplierAdapter.java
index 2c65f8e85c5f..14cbecb4f29b 100644
--- a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/internal/RequestDataSupplierAdapter.java
+++ b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/internal/RequestDataSupplierAdapter.java
@@ -30,6 +30,7 @@
 import org.reactivestreams.Subscriber;
 import org.reactivestreams.Subscription;
 import software.amazon.awssdk.annotations.SdkInternalApi;
+import software.amazon.awssdk.crt.CrtRuntimeException;
 import software.amazon.awssdk.crt.http.HttpHeader;
 import software.amazon.awssdk.http.SdkHttpResponse;
 import software.amazon.awssdk.utils.Logger;
@@ -49,8 +50,7 @@ public final class RequestDataSupplierAdapter implements RequestDataSupplier {
 
     private final Publisher<ByteBuffer> bodyPublisher;
 
-    // Not volatile, we synchronize on the subscriptionQueue
-    private Subscription subscription;
+    private volatile Subscription subscription;
 
     // TODO: not volatile since it's read and written only by CRT thread(s). Need to
     // ensure that CRT actually ensures consistency across their threads...
@@ -175,6 +175,20 @@ public boolean resetPosition() {
         return true;
     }
 
+    @Override
+    public void onException(CrtRuntimeException e) {
+        if (subscription != null) {
+            subscription.cancel();
+        }
+    }
+
+    @Override
+    public void onFinished() {
+        if (subscription != null) {
+            subscription.cancel();
+        }
+    }
+
     private Event takeFirstEvent() {
         try {
             return eventBuffer.takeFirst();
diff --git a/services-custom/s3-transfer-manager/src/test/java/software/amazon/awssdk/transfer/s3/internal/RequestDataSupplierAdapterTest.java b/services-custom/s3-transfer-manager/src/test/java/software/amazon/awssdk/transfer/s3/internal/RequestDataSupplierAdapterTest.java
index 87f5d2af82a3..b01cada9e1c6 100644
--- a/services-custom/s3-transfer-manager/src/test/java/software/amazon/awssdk/transfer/s3/internal/RequestDataSupplierAdapterTest.java
+++ b/services-custom/s3-transfer-manager/src/test/java/software/amazon/awssdk/transfer/s3/internal/RequestDataSupplierAdapterTest.java
@@ -17,18 +17,24 @@
 
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
 
 import io.reactivex.Flowable;
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 import org.junit.Test;
 import org.reactivestreams.Publisher;
 import org.reactivestreams.Subscriber;
+import org.reactivestreams.Subscription;
 import software.amazon.awssdk.core.async.AsyncRequestBody;
+import software.amazon.awssdk.crt.CrtRuntimeException;
 
 public class RequestDataSupplierAdapterTest {
 
@@ -156,4 +162,56 @@ public void subscribe(Subscriber<? super ByteBuffer> subscriber) {
             assertThat(readBuffer).isEqualTo(expectedBufferContent);
         }
     }
+
+    @Test
+    public void onException_cancelsSubscription() {
+        Subscription subscription = mock(Subscription.class);
+
+        AsyncRequestBody requestBody = new AsyncRequestBody() {
+            @Override
+            public Optional<Long> contentLength() {
+                return Optional.empty();
+            }
+
+            @Override
+            public void subscribe(Subscriber<? super ByteBuffer> subscriber) {
+                subscriber.onSubscribe(subscription);
+            }
+        };
+
+        RequestDataSupplierAdapter adapter = new RequestDataSupplierAdapter(requestBody);
+
+        // getRequestBytes() triggers a subscribe() on the publisher
+        adapter.getRequestBytes(ByteBuffer.allocate(0));
+
+        adapter.onException(new CrtRuntimeException("error"));
+
+        verify(subscription).cancel();
+    }
+
+    @Test
+    public void onFinished_cancelsSubscription() {
+        Subscription subscription = mock(Subscription.class);
+
+        AsyncRequestBody requestBody = new AsyncRequestBody() {
+            @Override
+            public Optional<Long> contentLength() {
+                return Optional.empty();
+            }
+
+            @Override
+            public void subscribe(Subscriber<? super ByteBuffer> subscriber) {
+                subscriber.onSubscribe(subscription);
+            }
+        };
+
+        RequestDataSupplierAdapter adapter = new RequestDataSupplierAdapter(requestBody);
+
+        // getRequestBytes() triggers a subscribe() on the publisher
+        adapter.getRequestBytes(ByteBuffer.allocate(0));
+
+        adapter.onFinished();
+
+        verify(subscription).cancel();
+    }
 }