diff --git a/src/main/scala/net/kemitix/s3thorp/Sync.scala b/src/main/scala/net/kemitix/s3thorp/Sync.scala
index 919c554..a95421c 100644
--- a/src/main/scala/net/kemitix/s3thorp/Sync.scala
+++ b/src/main/scala/net/kemitix/s3thorp/Sync.scala
@@ -17,7 +17,7 @@ class Sync(s3Client: S3Client)
   override def objectHead(bucket: Bucket, remoteKey: RemoteKey)=
     s3Client.objectHead(bucket, remoteKey)
 
-  override def upload(localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey): IO[Unit] =
+  override def upload(localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey) =
     s3Client.upload(localFile, bucket, remoteKey)
 
   def run(c: Config): IO[Unit] = for {
diff --git a/src/main/scala/net/kemitix/s3thorp/awssdk/S3Client.scala b/src/main/scala/net/kemitix/s3thorp/awssdk/S3Client.scala
index 5c788cb..e5ea8d8 100644
--- a/src/main/scala/net/kemitix/s3thorp/awssdk/S3Client.scala
+++ b/src/main/scala/net/kemitix/s3thorp/awssdk/S3Client.scala
@@ -8,7 +8,7 @@ trait S3Client {
 
   def objectHead(bucket: Bucket, remoteKey: RemoteKey): IO[Option[(MD5Hash, LastModified)]]
 
-  def upload(localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey): IO[Unit]
+  def upload(localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey): IO[Either[Throwable, MD5Hash]]
 
 }
 
diff --git a/src/main/scala/net/kemitix/s3thorp/awssdk/ThropS3Client.scala b/src/main/scala/net/kemitix/s3thorp/awssdk/ThropS3Client.scala
index 6287f3e..934e2ca 100644
--- a/src/main/scala/net/kemitix/s3thorp/awssdk/ThropS3Client.scala
+++ b/src/main/scala/net/kemitix/s3thorp/awssdk/ThropS3Client.scala
@@ -2,13 +2,13 @@ package net.kemitix.s3thorp.awssdk
 
 import cats.effect.IO
 import com.github.j5ik2o.reactive.aws.s3.cats.S3CatsIOClient
-import net.kemitix.s3thorp.Sync.{Bucket, LastModified, LocalFile, MD5Hash, RemoteKey}
+import net.kemitix.s3thorp.Sync._
 import software.amazon.awssdk.core.async.AsyncRequestBody
 import software.amazon.awssdk.services.s3.model.{HeadObjectRequest, PutObjectRequest}
 
 private class ThropS3Client(s3Client: S3CatsIOClient) extends S3Client {
 
-  def objectHead(bucket: Bucket, remoteKey: RemoteKey): IO[Option[(MD5Hash, LastModified)]] = {
+  def objectHead(bucket: Bucket, remoteKey: RemoteKey) = {
     val request = HeadObjectRequest.builder().bucket(bucket).key(remoteKey).build()
     s3Client.headObject(request).attempt.map {
       case Right(response) => Some((response.eTag(), response.lastModified()))
@@ -16,12 +16,10 @@ private class ThropS3Client(s3Client: S3CatsIOClient) extends S3Client {
     }
   }
 
-  def upload(localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey): IO[Unit] = {
+  def upload(localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey): IO[Either[Throwable, MD5Hash]] = {
     val request = PutObjectRequest.builder().bucket(bucket).key(remoteKey).build()
     val body = AsyncRequestBody.fromFile(localFile)
-    for {
-      _ <- s3Client.putObject(request, body)
-    } yield ()
+    s3Client.putObject(request, body).map{response => Right(response.eTag())}
   }
 
 }
diff --git a/src/test/scala/net/kemitix/s3thorp/DummyS3Client.scala b/src/test/scala/net/kemitix/s3thorp/DummyS3Client.scala
index 78f86be..a83bdbd 100644
--- a/src/test/scala/net/kemitix/s3thorp/DummyS3Client.scala
+++ b/src/test/scala/net/kemitix/s3thorp/DummyS3Client.scala
@@ -8,5 +8,5 @@ trait DummyS3Client extends S3Client {
 
   override def objectHead(bucket: Bucket, remoteKey: RemoteKey): IO[Option[(MD5Hash, LastModified)]] = ???
 
-  override def upload(localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey): IO[Unit] = ???
+  override def upload(localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey): IO[Either[Throwable, MD5Hash]] = ???
 }
diff --git a/src/test/scala/net/kemitix/s3thorp/S3UploaderSuite.scala b/src/test/scala/net/kemitix/s3thorp/S3UploaderSuite.scala
index 976a9f4..5c1afd1 100644
--- a/src/test/scala/net/kemitix/s3thorp/S3UploaderSuite.scala
+++ b/src/test/scala/net/kemitix/s3thorp/S3UploaderSuite.scala
@@ -3,14 +3,16 @@ package net.kemitix.s3thorp
 import java.io.File
 
 import cats.effect.IO
-import net.kemitix.s3thorp.Sync.{Bucket, LastModified, LocalFile, MD5Hash, RemoteKey}
+import net.kemitix.s3thorp.Sync.{Bucket, LocalFile, RemoteKey}
 import org.scalatest.FunSpec
 
 class S3UploaderSuite extends FunSpec {
 
   new S3Uploader {
-    override def objectHead(bucket: String, key: String): IO[Option[(MD5Hash, LastModified)]] = ???
-    override def upload(localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey): IO[Unit] = IO.unit
+    val md5Hash = "the-md5hash"
+    override def objectHead(bucket: String, key: String) = ???
+    override def upload(localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey) =
+      IO(Right(md5Hash))
 
     describe("upload") {
       val config: Config = Config("bucket", "prefix", new File("/path/to/files"))
diff --git a/src/test/scala/net/kemitix/s3thorp/awssdk/S3ClientSuite.scala b/src/test/scala/net/kemitix/s3thorp/awssdk/S3ClientSuite.scala
index 8479fbb..e4d63c0 100644
--- a/src/test/scala/net/kemitix/s3thorp/awssdk/S3ClientSuite.scala
+++ b/src/test/scala/net/kemitix/s3thorp/awssdk/S3ClientSuite.scala
@@ -4,11 +4,10 @@ import java.io.File
 import java.time.Instant
 
 import cats.effect.IO
-import com.github.j5ik2o.reactive.aws.s3.S3AsyncClient
 import com.github.j5ik2o.reactive.aws.s3.cats.S3CatsIOClient
 import net.kemitix.s3thorp.Sync.{Bucket, LocalFile, RemoteKey}
 import org.scalatest.FunSpec
-import software.amazon.awssdk.services.s3.model.{HeadObjectRequest, HeadObjectResponse, NoSuchKeyException, PutObjectRequest, PutObjectResponse}
+import software.amazon.awssdk.services.s3.model._
 
 class S3ClientSuite extends FunSpec {
 
@@ -44,19 +43,21 @@ class S3ClientSuite extends FunSpec {
 
   }
 
-
   describe("upload") {
+    def invoke(s3Client: ThropS3Client, localFile: LocalFile, bucket: Bucket, remoteKey: RemoteKey) =
+      s3Client.upload(localFile, bucket, remoteKey).unsafeRunSync
     describe("when uploading a file") {
+      val md5Hash = "the-md5hash"
       val s3Client = new ThropS3Client(
         new S3CatsIOClient with JavaClientWrapper {
           override def putObject(putObjectRequest: PutObjectRequest, requestBody: RB) =
-            IO(PutObjectResponse.builder().build())
+            IO(PutObjectResponse.builder().eTag(md5Hash).build())
         })
       val localFile: LocalFile = new File("/some/file")
       val bucket: Bucket = "a-bucket"
       val remoteKey: RemoteKey = "prefix/file"
-      it("should not throw any exceptions") {
-        s3Client.upload(localFile, bucket, remoteKey)
+      it("should return hash of uploaded file") {
+        assertResult(Right(md5Hash))(invoke(s3Client, localFile, bucket, remoteKey))
       }
     }
   }