diff --git a/backend/posix/posix.go b/backend/posix/posix.go
index 3d4765e6..f7c0b370 100644
--- a/backend/posix/posix.go
+++ b/backend/posix/posix.go
@@ -1470,7 +1470,11 @@ func (p *Posix) CompleteMultipartUploadWithCopy(ctx context.Context, input *s3.C
 	if err != nil && !errors.Is(err, meta.ErrNoSuchKey) {
 		return res, "", fmt.Errorf("get mp checksums: %w", err)
 	}
-	var checksumAlgorithm types.ChecksumAlgorithm
+
+	// The checksum algorithm should default to CRC64NVME
+	// just for data integrity. It isn't going to be saved
+	// in the final object metadata
+	checksumAlgorithm := types.ChecksumAlgorithmCrc64nvme
 	if checksums.Algorithm != "" {
 		checksumAlgorithm = checksums.Algorithm
 	}
@@ -1485,6 +1489,15 @@ func (p *Posix) CompleteMultipartUploadWithCopy(ctx context.Context, input *s3.C
 		return res, "", s3err.GetChecksumTypeMismatchOnMpErr(checksumType)
 	}
 
+	// The checksum type should default to FULL_OBJECT(crc64nvme)
+	checksumType := checksums.Type
+	if checksums.Type == "" {
+		// do not modify checksums.Type to further not save the checksum
+		// in the final object. As if no checksum has been specified on mp
+		// creation, the final object shouldn't contain the checksum metadata
+		checksumType = types.ChecksumTypeFullObject
+	}
+
 	// check all parts ok
 	last := len(parts) - 1
 	var totalsize int64
@@ -1551,7 +1564,7 @@ func (p *Posix) CompleteMultipartUploadWithCopy(ctx context.Context, input *s3.C
 
 	var hashRdr *utils.HashReader
 	var compositeChecksumRdr *utils.CompositeChecksumReader
-	switch checksums.Type {
+	switch checksumType {
 	case types.ChecksumTypeFullObject:
 		if !composableCRC {
 			hashRdr, err = utils.NewHashReader(nil, "", utils.HashType(strings.ToLower(string(checksumAlgorithm))))
@@ -1591,7 +1604,7 @@ func (p *Posix) CompleteMultipartUploadWithCopy(ctx context.Context, input *s3.C
 		}
 
 		var rdr io.Reader = pf
-		switch checksums.Type {
+		switch checksumType {
 		case types.ChecksumTypeFullObject:
 			if composableCRC {
 				if i == 0 {
@@ -1778,6 +1791,14 @@ func (p *Posix) CompleteMultipartUploadWithCopy(ctx context.Context, input *s3.C
 		if err != nil {
 			return res, "", fmt.Errorf("store object checksum: %w", err)
 		}
+	} else {
+		// in this case no checksum has been specified on mp creation
+		// and the complete request checksum is defaulted to crc64nvem
+		// simply calculated the sum to further retrun in the response
+		if hashRdr != nil {
+			sum := hashRdr.Sum()
+			crc64nvme = &sum
+		}
 	}
 
 	// load and set retention
@@ -1820,7 +1841,7 @@ func (p *Posix) CompleteMultipartUploadWithCopy(ctx context.Context, input *s3.C
 		ChecksumSHA1:      sha1,
 		ChecksumSHA256:    sha256,
 		ChecksumCRC64NVME: crc64nvme,
-		ChecksumType:      &checksums.Type,
+		ChecksumType:      &checksumType,
 	}, versionID, nil
 }
 
diff --git a/tests/integration/tests.go b/tests/integration/tests.go
index 0180f408..20543752 100644
--- a/tests/integration/tests.go
+++ b/tests/integration/tests.go
@@ -12970,7 +12970,7 @@ func CompleteMultipartUpload_should_ignore_the_final_checksum(s *S3Conf) error {
 			MultipartUpload: &types.CompletedMultipartUpload{
 				Parts: cParts,
 			},
-			ChecksumSHA1: getPtr("Kq5sNclPz7QV2+lfQIuc6R7oRu0="), // should ignore this
+			ChecksumCRC64NVME: getPtr("vqf3hRLTlJw="), // should ignore this
 		})
 		cancel()
 		if err != nil {
@@ -12993,9 +12993,10 @@ func CompleteMultipartUpload_should_ignore_the_final_checksum(s *S3Conf) error {
 			return fmt.Errorf("expected nil sha256 checksum, insted got %v",
 				*res.ChecksumSHA256)
 		}
-		if res.ChecksumCRC64NVME != nil {
-			return fmt.Errorf("expected nil crc64nvme checksum, insted got %v",
-				*res.ChecksumSHA256)
+		// If no checksum is specified on mp creation, it should default
+		// to crc64nvme
+		if res.ChecksumCRC64NVME == nil {
+			return fmt.Errorf("expected non nil crc64nvme checksum")
 		}
 
 		return nil
@@ -24659,9 +24660,8 @@ func Versioning_WORM_CompleteMultipartUpload_overwrite_locked_object(s *S3Conf)
 			MultipartUpload: &types.CompletedMultipartUpload{
 				Parts: []types.CompletedPart{
 					{
-						ETag:              part.ETag,
-						PartNumber:        part.PartNumber,
-						ChecksumCRC64NVME: part.ChecksumCRC64NVME,
+						ETag:       part.ETag,
+						PartNumber: part.PartNumber,
 					},
 				},
 			},
@@ -24679,7 +24679,6 @@ func Versioning_WORM_CompleteMultipartUpload_overwrite_locked_object(s *S3Conf)
 			Size:         &dataLen,
 			VersionId:    res.VersionId,
 			StorageClass: types.ObjectVersionStorageClassStandard,
-			ChecksumType: res.ChecksumType,
 		}
 
 		result := []types.ObjectVersion{version, v}
diff --git a/tests/integration/utils.go b/tests/integration/utils.go
index 308f855b..0010c098 100644
--- a/tests/integration/utils.go
+++ b/tests/integration/utils.go
@@ -518,7 +518,7 @@ func putObjectWithData(lgth int64, input *s3.PutObjectInput, client *s3.Client)
 		input.Body = r
 	}
 
-	ctx, cancel := context.WithTimeout(context.Background(), shortTimeout)
+	ctx, cancel := context.WithTimeout(context.Background(), longTimeout)
 	res, err := client.PutObject(ctx, input)
 	cancel()
 	if err != nil {