diff --git a/backend/azure/azure.go b/backend/azure/azure.go
index 413cf3b..27a433d 100644
--- a/backend/azure/azure.go
+++ b/backend/azure/azure.go
@@ -1201,6 +1201,7 @@ func (az *Azure) CompleteMultipartUpload(ctx context.Context, input *s3.Complete
 		return ptNumber - nextPtNumber
 	})
 
+	last := len(blockList.UncommittedBlocks) - 1
 	for i, block := range blockList.UncommittedBlocks {
 		ptNumber, err := decodeBlockId(*block.Name)
 		if err != nil {
@@ -1213,6 +1214,11 @@ func (az *Azure) CompleteMultipartUpload(ctx context.Context, input *s3.Complete
 		if *input.MultipartUpload.Parts[i].PartNumber != int32(ptNumber) {
 			return nil, s3err.GetAPIError(s3err.ErrInvalidPart)
 		}
+		// all parts except the last need to be greater, thena
+		// the minimum allowed size (5 Mib)
+		if i < last && *block.Size < backend.MinPartSize {
+			return nil, s3err.GetAPIError(s3err.ErrEntityTooSmall)
+		}
 		blockIds = append(blockIds, *block.Name)
 	}
 
diff --git a/backend/common.go b/backend/common.go
index 60a144c..b1e44f1 100644
--- a/backend/common.go
+++ b/backend/common.go
@@ -34,6 +34,9 @@ const (
 	// this is the media type for directories in AWS and Nextcloud
 	DirContentType     = "application/x-directory"
 	DefaultContentType = "binary/octet-stream"
+
+	// this is the minimum allowed size for mp parts
+	MinPartSize = 5 * 1024 * 1024
 )
 
 func IsValidBucketName(name string) bool { return true }
diff --git a/backend/posix/posix.go b/backend/posix/posix.go
index 53ad238..ee1c167 100644
--- a/backend/posix/posix.go
+++ b/backend/posix/posix.go
@@ -1375,7 +1375,6 @@ func (p *Posix) CompleteMultipartUpload(ctx context.Context, input *s3.CompleteM
 
 	// check all parts ok
 	last := len(parts) - 1
-	partsize := int64(0)
 	var totalsize int64
 	for i, part := range parts {
 		if part.PartNumber == nil || *part.PartNumber < 1 {
@@ -1389,13 +1388,11 @@ func (p *Posix) CompleteMultipartUpload(ctx context.Context, input *s3.CompleteM
 			return nil, s3err.GetAPIError(s3err.ErrInvalidPart)
 		}
 
-		if i == 0 {
-			partsize = fi.Size()
-		}
 		totalsize += fi.Size()
-		// all parts except the last need to be the same size
-		if i < last && partsize != fi.Size() {
-			return nil, s3err.GetAPIError(s3err.ErrInvalidPart)
+		// all parts except the last need to be greater, thena
+		// the minimum allowed size (5 Mib)
+		if i < last && fi.Size() < backend.MinPartSize {
+			return nil, s3err.GetAPIError(s3err.ErrEntityTooSmall)
 		}
 
 		b, err := p.meta.RetrieveAttribute(nil, bucket, partObjPath, etagkey)
diff --git a/tests/integration/group-tests.go b/tests/integration/group-tests.go
index 1ecc64c..282da64 100644
--- a/tests/integration/group-tests.go
+++ b/tests/integration/group-tests.go
@@ -321,6 +321,7 @@ func TestCompleteMultipartUpload(s *S3Conf) {
 	CompletedMultipartUpload_non_existing_bucket(s)
 	CompleteMultipartUpload_invalid_part_number(s)
 	CompleteMultipartUpload_invalid_ETag(s)
+	CompleteMultipartUpload_small_upload_size(s)
 	CompleteMultipartUpload_empty_parts(s)
 	CompleteMultipartUpload_success(s)
 	if !s.azureTests {
@@ -856,7 +857,6 @@ func GetIntTests() IntTests {
 		"CompletedMultipartUpload_non_existing_bucket":                        CompletedMultipartUpload_non_existing_bucket,
 		"CompleteMultipartUpload_invalid_part_number":                         CompleteMultipartUpload_invalid_part_number,
 		"CompleteMultipartUpload_invalid_ETag":                                CompleteMultipartUpload_invalid_ETag,
-		"CompleteMultipartUpload_empty_parts":                                 CompleteMultipartUpload_empty_parts,
 		"CompleteMultipartUpload_success":                                     CompleteMultipartUpload_success,
 		"CompleteMultipartUpload_racey_success":                               CompleteMultipartUpload_racey_success,
 		"PutBucketAcl_non_existing_bucket":                                    PutBucketAcl_non_existing_bucket,
diff --git a/tests/integration/tests.go b/tests/integration/tests.go
index 9965e8d..08c7fb5 100644
--- a/tests/integration/tests.go
+++ b/tests/integration/tests.go
@@ -7192,6 +7192,49 @@ func CompleteMultipartUpload_invalid_ETag(s *S3Conf) error {
 	})
 }
 
+func CompleteMultipartUpload_small_upload_size(s *S3Conf) error {
+	testName := "CompleteMultipartUpload_small_upload_size"
+	return actionHandler(s, testName, func(s3client *s3.Client, bucket string) error {
+		obj := "my-obj"
+
+		mp, err := createMp(s3client, bucket, obj)
+		if err != nil {
+			return err
+		}
+
+		// The uploaded parts size is 256 < 5 Mib (the minimum allowed size)
+		parts, _, err := uploadParts(s3client, 1024, 4, bucket, obj, *mp.UploadId)
+		if err != nil {
+			return err
+		}
+
+		cParts := []types.CompletedPart{}
+
+		for _, el := range parts {
+			cParts = append(cParts, types.CompletedPart{
+				PartNumber: el.PartNumber,
+				ETag:       el.ETag,
+			})
+		}
+
+		ctx, cancel := context.WithTimeout(context.Background(), shortTimeout)
+		_, err = s3client.CompleteMultipartUpload(ctx, &s3.CompleteMultipartUploadInput{
+			Bucket:   &bucket,
+			Key:      &obj,
+			UploadId: mp.UploadId,
+			MultipartUpload: &types.CompletedMultipartUpload{
+				Parts: cParts,
+			},
+		})
+		cancel()
+		if err := checkApiErr(err, s3err.GetAPIError(s3err.ErrEntityTooSmall)); err != nil {
+			return err
+		}
+
+		return nil
+	})
+}
+
 func CompleteMultipartUpload_empty_parts(s *S3Conf) error {
 	testName := "CompleteMultipartUpload_empty_parts"
 	return actionHandler(s, testName, func(s3client *s3.Client, bucket string) error {
@@ -7233,7 +7276,7 @@ func CompleteMultipartUpload_success(s *S3Conf) error {
 			return err
 		}
 
-		objSize := int64(5 * 1024 * 1024)
+		objSize := int64(25 * 1024 * 1024)
 		parts, csum, err := uploadParts(s3client, objSize, 5, bucket, obj, *out.UploadId)
 		if err != nil {
 			return err
@@ -7326,7 +7369,7 @@ func CompleteMultipartUpload_racey_success(s *S3Conf) error {
 		var mu sync.RWMutex
 		uploads := make([]mpinfo, 10)
 		sums := make([]string, 10)
-		objSize := int64(5 * 1024 * 1024)
+		objSize := int64(25 * 1024 * 1024)
 
 		eg := errgroup.Group{}
 		for i := 0; i < 10; i++ {
@@ -12990,7 +13033,7 @@ func Versioning_Multipart_Upload_success(s *S3Conf) error {
 			return err
 		}
 
-		objSize := int64(5 * 1024 * 1024)
+		objSize := int64(25 * 1024 * 1024)
 		parts, _, err := uploadParts(s3client, objSize, 5, bucket, obj, *out.UploadId)
 		if err != nil {
 			return err
@@ -13070,7 +13113,7 @@ func Versioning_Multipart_Upload_overwrite_an_object(s *S3Conf) error {
 			return err
 		}
 
-		objSize := int64(5 * 1024 * 1024)
+		objSize := int64(25 * 1024 * 1024)
 		parts, _, err := uploadParts(s3client, objSize, 5, bucket, obj, *out.UploadId)
 		if err != nil {
 			return err
diff --git a/tests/test_s3api_multipart.sh b/tests/test_s3api_multipart.sh
index e5e10de..05a5583 100755
--- a/tests/test_s3api_multipart.sh
+++ b/tests/test_s3api_multipart.sh
@@ -54,7 +54,7 @@ source ./tests/commands/list_multipart_uploads.sh
   run create_test_files "$bucket_file"
   assert_success
 
-  run dd if=/dev/urandom of="$TEST_FILE_FOLDER/$bucket_file" bs=5M count=1
+  run dd if=/dev/urandom of="$TEST_FILE_FOLDER/$bucket_file" bs=20M count=1
   assert_success
 
   run setup_bucket "s3api" "$BUCKET_ONE_NAME"
@@ -115,7 +115,7 @@ source ./tests/commands/list_multipart_uploads.sh
   run create_test_file "$bucket_file"
   assert_success
 
-  run dd if=/dev/urandom of="$TEST_FILE_FOLDER/$bucket_file" bs=5M count=1
+  run dd if=/dev/urandom of="$TEST_FILE_FOLDER/$bucket_file" bs=20M count=1
   assert_success
 
   run setup_bucket "s3api" "$BUCKET_ONE_NAME"
diff --git a/tests/util/util_multipart.sh b/tests/util/util_multipart.sh
index 5a7a3f4..0118abd 100644
--- a/tests/util/util_multipart.sh
+++ b/tests/util/util_multipart.sh
@@ -315,7 +315,7 @@ setup_multipart_upload_with_params() {
     return 1
   fi
 
-  if ! result=$(dd if=/dev/urandom of="$TEST_FILE_FOLDER/$2" bs=5M count=1 2>&1); then
+  if ! result=$(dd if=/dev/urandom of="$TEST_FILE_FOLDER/$2" bs=20M count=1 2>&1); then
     log 2 "error creating large file: $result"
     return 1
   fi