diff --git a/backend.go b/backend.go
index bb5cc5e..f5334b1 100644
--- a/backend.go
+++ b/backend.go
@@ -1,7 +1,6 @@
 package gofakes3
 
 import (
-	"encoding/hex"
 	"io"
 	"time"
 
@@ -120,17 +119,6 @@ func (p ListBucketPage) IsEmpty() bool {
 	return p == ListBucketPage{}
 }
 
-type PutObjectResult struct {
-	// If versioning is enabled on the bucket, this should be set to the
-	// created version ID. If versioning is not enabled, this should be
-	// empty.
-	VersionID VersionID
-
-	// ETag is the value of the ETag header returned by the backend, stripped of
-	// its quotation marks.
-	ETag string
-}
-
 // Backend provides a set of operations to be implemented in order to support
 // gofakes3.
 //
@@ -324,13 +312,13 @@ type VersionedBackend interface {
 // gets finalised and pushed to the backend.
 type MultipartBackend interface {
 	CreateMultipartUpload(bucket, object string, meta map[string]string) (UploadID, error)
-	UploadPart(bucket, object string, id UploadID, partNumber int, contentLength int64, input io.Reader) (etag string, err error)
+	UploadPart(bucket, object string, id UploadID, partNumber int, contentLength int64, input io.Reader) (*UploadPartResult, error)
 
 	ListMultipartUploads(bucket string, marker *UploadListMarker, prefix Prefix, limit int64) (*ListMultipartUploadsResult, error)
 	ListParts(bucket, object string, uploadID UploadID, marker int, limit int64) (*ListMultipartUploadPartsResult, error)
 
 	AbortMultipartUpload(bucket, object string, id UploadID) error
-	CompleteMultipartUpload(bucket, object string, id UploadID, input *CompleteMultipartUploadRequest) (versionID VersionID, etag string, err error)
+	CompleteMultipartUpload(bucket, object string, id UploadID, input *CompleteMultipartUploadRequest) (*CompleteMultipartResult, error)
 }
 
 // CopyObject is a helper function useful for quickly implementing CopyObject on
@@ -343,13 +331,13 @@ func CopyObject(db Backend, srcBucket, srcKey, dstBucket, dstKey string, meta ma
 	}
 	defer c.Contents.Close()
 
-	_, err = db.PutObject(dstBucket, dstKey, meta, c.Contents, c.Size)
+	res, err := db.PutObject(dstBucket, dstKey, meta, c.Contents, c.Size)
 	if err != nil {
 		return
 	}
 
 	return CopyObjectResult{
-		ETag:         `"` + hex.EncodeToString(c.Hash) + `"`,
+		ETag:         res.ETag,
 		LastModified: NewContentTime(time.Now()),
 	}, nil
 }
diff --git a/gofakes3.go b/gofakes3.go
index b4d7468..8fe0456 100644
--- a/gofakes3.go
+++ b/gofakes3.go
@@ -663,7 +663,11 @@ func (g *GoFakeS3) createObjectBrowserUpload(bucket string, w http.ResponseWrite
 		w.Header().Set("x-amz-version-id", string(result.VersionID))
 	}
 
-	w.Header().Set("ETag", `"`+hex.EncodeToString(rdr.Sum(nil))+`"`)
+	etag := result.ETag
+	if etag == "" {
+		etag = formatETag(hex.EncodeToString(rdr.Sum(nil)))
+	}
+	w.Header().Set("ETag", etag)
 	return nil
 }
 
@@ -728,9 +732,9 @@ func (g *GoFakeS3) createObject(bucket, object string, w http.ResponseWriter, r
 
 	etag := result.ETag
 	if etag == "" {
-		etag = hex.EncodeToString(rdr.Sum(nil))
+		etag = formatETag(hex.EncodeToString(rdr.Sum(nil)))
 	}
-	w.Header().Set("ETag", fmt.Sprintf("\"%s\"", etag))
+	w.Header().Set("ETag", etag)
 
 	return nil
 }
@@ -953,7 +957,7 @@ func (g *GoFakeS3) putMultipartUploadPart(bucket, object string, uploadID Upload
 		return err
 	}
 
-	w.Header().Add("ETag", etag)
+	w.Header().Add("ETag", formatETag(etag))
 	return nil
 }
 
@@ -974,17 +978,17 @@ func (g *GoFakeS3) completeMultipartUpload(bucket, object string, uploadID Uploa
 		return err
 	}
 
-	versionID, etag, err := g.uploader.CompleteMultipartUpload(bucket, object, uploadID, &in)
+	res, err := g.uploader.CompleteMultipartUpload(bucket, object, uploadID, &in)
 	if err != nil {
 		return err
 	}
 
-	if versionID != "" {
-		w.Header().Set("x-amz-version-id", string(versionID))
+	if res.VersionID != "" {
+		w.Header().Set("x-amz-version-id", string(res.VersionID))
 	}
 
 	return g.xmlEncoder(w).Encode(&CompleteMultipartUploadResult{
-		ETag:   etag,
+		ETag:   res.ETag,
 		Bucket: bucket,
 		Key:    object,
 	})
@@ -1210,3 +1214,7 @@ func listBucketVersionsPageFromQuery(query url.Values) (page ListBucketVersionsP
 
 	return page, nil
 }
+
+func formatETag(etag string) string {
+	return fmt.Sprintf("\"%s\"", etag)
+}
diff --git a/messages.go b/messages.go
index 17138fe..6d51a2f 100644
--- a/messages.go
+++ b/messages.go
@@ -365,6 +365,20 @@ func (b *ListBucketVersionsResult) AddPrefix(prefix string) {
 	b.CommonPrefixes = append(b.CommonPrefixes, CommonPrefix{Prefix: prefix})
 }
 
+type UploadPartResult struct {
+	ETag string `xml:"ETag,omitempty"`
+}
+
+type CompleteMultipartResult struct {
+	// If versioning is enabled on the bucket, this should be set to the
+	// created version ID. If versioning is not enabled, this should be
+	// empty.
+	VersionID VersionID `xml:"VersionId,omitempty"`
+
+	// ETag is the value of the ETag header returned by the backend.
+	ETag string `xml:"ETag,omitempty"`
+}
+
 type ListMultipartUploadsResult struct {
 	Bucket string `xml:"Bucket"`
 
@@ -430,6 +444,17 @@ type ListMultipartUploadPartItem struct {
 	Size         int64       `xml:"Size"`
 }
 
+// PutObjectResult contains the response from a PutObject operation.
+type PutObjectResult struct {
+	// If versioning is enabled on the bucket, this should be set to the
+	// created version ID. If versioning is not enabled, this should be
+	// empty.
+	VersionID VersionID `xml:"VersionId,omitempty"`
+
+	// ETag is the value of the ETag header returned by the backend.
+	ETag string `xml:"ETag,omitempty"`
+}
+
 // CopyObjectResult contains the response from a CopyObject operation.
 type CopyObjectResult struct {
 	XMLName      xml.Name    `xml:"CopyObjectResult"`
diff --git a/uploader.go b/uploader.go
index 48b3af2..c77cb85 100644
--- a/uploader.go
+++ b/uploader.go
@@ -367,17 +367,17 @@ func (u *uploader) AbortMultipartUpload(bucket, object string, id UploadID) erro
 	return nil
 }
 
-func (u *uploader) UploadPart(bucket, object string, id UploadID, partNumber int, contentLength int64, input io.Reader) (etag string, err error) {
+func (u *uploader) UploadPart(bucket, object string, id UploadID, partNumber int, contentLength int64, input io.Reader) (*UploadPartResult, error) {
 	body, err := io.ReadAll(input)
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 	if len(body) != int(contentLength) {
-		return "", ErrIncompleteBody
+		return nil, ErrIncompleteBody
 	}
 	mpu, err := u.getUnlocked(bucket, object, id)
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 
 	mpu.mu.Lock()
@@ -387,7 +387,7 @@ func (u *uploader) UploadPart(bucket, object string, id UploadID, partNumber int
 	// from guaranteed unique input:
 	hash := md5.New()
 	hash.Write([]byte(body))
-	etag = fmt.Sprintf(`"%s"`, hex.EncodeToString(hash.Sum(nil)))
+	etag := fmt.Sprintf(`"%s"`, hex.EncodeToString(hash.Sum(nil)))
 
 	part := multipartUploadPart{
 		PartNumber:   partNumber,
@@ -399,13 +399,14 @@ func (u *uploader) UploadPart(bucket, object string, id UploadID, partNumber int
 		mpu.parts = append(mpu.parts, make([]*multipartUploadPart, partNumber-len(mpu.parts)+1)...)
 	}
 	mpu.parts[partNumber] = &part
-	return etag, nil
+
+	return &UploadPartResult{ETag: formatETag(etag)}, nil
 }
 
-func (u *uploader) CompleteMultipartUpload(bucket, object string, id UploadID, input *CompleteMultipartUploadRequest) (version VersionID, etag string, err error) {
+func (u *uploader) CompleteMultipartUpload(bucket, object string, id UploadID, input *CompleteMultipartUploadRequest) (*CompleteMultipartResult, error) {
 	mpu, err := u.getUnlocked(bucket, object, id)
 	if err != nil {
-		return "", "", err
+		return nil, err
 	}
 
 	mpu.mu.Lock()
@@ -417,23 +418,23 @@ func (u *uploader) CompleteMultipartUpload(bucket, object string, id UploadID, i
 	// end up uploading more parts than you need to assemble, so it should
 	// probably just ignore that?
 	if len(input.Parts) > mpuPartsLen {
-		return "", "", ErrInvalidPart
+		return nil, ErrInvalidPart
 	}
 
 	if !input.partsAreSorted() {
-		return "", "", ErrInvalidPartOrder
+		return nil, ErrInvalidPartOrder
 	}
 
 	var size int64
 
 	for _, inPart := range input.Parts {
 		if inPart.PartNumber >= mpuPartsLen || mpu.parts[inPart.PartNumber] == nil {
-			return "", "", ErrorMessagef(ErrInvalidPart, "unexpected part number %d in complete request", inPart.PartNumber)
+			return nil, ErrorMessagef(ErrInvalidPart, "unexpected part number %d in complete request", inPart.PartNumber)
 		}
 
 		upPart := mpu.parts[inPart.PartNumber]
 		if strings.Trim(inPart.ETag, "\"") != strings.Trim(upPart.ETag, "\"") {
-			return "", "", ErrorMessagef(ErrInvalidPart, "unexpected part etag for number %d in complete request", inPart.PartNumber)
+			return nil, ErrorMessagef(ErrInvalidPart, "unexpected part etag for number %d in complete request", inPart.PartNumber)
 		}
 
 		size += int64(len(upPart.Body))
@@ -444,16 +445,22 @@ func (u *uploader) CompleteMultipartUpload(bucket, object string, id UploadID, i
 		body = append(body, mpu.parts[part.PartNumber].Body...)
 	}
 
-	hash := fmt.Sprintf("%x", md5.Sum(body))
-
 	result, err := u.storage.PutObject(bucket, object, mpu.Meta, bytes.NewReader(body), int64(len(body)))
 	if err != nil {
-		return "", "", err
+		return nil, err
+	}
+
+	etag := result.ETag
+	if etag == "" {
+		etag = formatETag(fmt.Sprintf("%x", md5.Sum(body)))
 	}
 
 	// if getUnlocked succeeded, so will this:
 	u.buckets[bucket].remove(id)
-	return result.VersionID, hash, nil
+	return &CompleteMultipartResult{
+		VersionID: result.VersionID,
+		ETag:      etag,
+	}, nil
 }
 
 func (u *uploader) getUnlocked(bucket, object string, id UploadID) (mu *multipartUpload, err error) {