diff --git a/backend/opendrive/opendrive.go b/backend/opendrive/opendrive.go
index 6240ecf95..ddeab9546 100644
--- a/backend/opendrive/opendrive.go
+++ b/backend/opendrive/opendrive.go
@@ -1,11 +1,9 @@
 package opendrive
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"io"
-	"mime/multipart"
 	"net/http"
 	"net/url"
 	"path"
@@ -947,84 +945,35 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 		fs.Debugf(o, "Uploading chunk %d, size=%d, remain=%d", chunkCounter, currentChunkSize, remainingBytes)
 
 		chunk := readers.NewRepeatableLimitReaderBuffer(in, buf, currentChunkSize)
+		var reply uploadFileChunkReply
 		err = o.fs.pacer.Call(func() (bool, error) {
 			// seek to the start in case this is a retry
 			if _, err = chunk.Seek(0, io.SeekStart); err != nil {
 				return false, err
 			}
-			var formBody bytes.Buffer
-			w := multipart.NewWriter(&formBody)
-			fw, err := w.CreateFormFile("file_data", o.remote)
-			if err != nil {
-				return false, err
-			}
-			if _, err = io.Copy(fw, chunk); err != nil {
-				return false, err
-			}
-			// Add session_id
-			if fw, err = w.CreateFormField("session_id"); err != nil {
-				return false, err
-			}
-			if _, err = fw.Write([]byte(o.fs.session.SessionID)); err != nil {
-				return false, err
-			}
-			// Add session_id
-			if fw, err = w.CreateFormField("session_id"); err != nil {
-				return false, err
-			}
-			if _, err = fw.Write([]byte(o.fs.session.SessionID)); err != nil {
-				return false, err
-			}
-			// Add file_id
-			if fw, err = w.CreateFormField("file_id"); err != nil {
-				return false, err
-			}
-			if _, err = fw.Write([]byte(o.id)); err != nil {
-				return false, err
-			}
-			// Add temp_location
-			if fw, err = w.CreateFormField("temp_location"); err != nil {
-				return false, err
-			}
-			if _, err = fw.Write([]byte(openResponse.TempLocation)); err != nil {
-				return false, err
-			}
-			// Add chunk_offset
-			if fw, err = w.CreateFormField("chunk_offset"); err != nil {
-				return false, err
-			}
-			if _, err = fw.Write([]byte(strconv.FormatInt(chunkOffset, 10))); err != nil {
-				return false, err
-			}
-			// Add chunk_size
-			if fw, err = w.CreateFormField("chunk_size"); err != nil {
-				return false, err
-			}
-			if _, err = fw.Write([]byte(strconv.FormatInt(currentChunkSize, 10))); err != nil {
-				return false, err
-			}
-			// Don't forget to close the multipart writer.
-			// If you don't close it, your request will be missing the terminating boundary.
-			err = w.Close()
-			if err != nil {
-				return false, err
-			}
-
 			opts := rest.Opts{
-				Method:       "POST",
-				Path:         "/upload/upload_file_chunk.json",
-				Body:         &formBody,
-				ExtraHeaders: map[string]string{"Content-Type": w.FormDataContentType()},
+				Method: "POST",
+				Path:   "/upload/upload_file_chunk.json",
+				Body:   chunk,
+				MultipartParams: url.Values{
+					"session_id":    []string{o.fs.session.SessionID},
+					"file_id":       []string{o.id},
+					"temp_location": []string{openResponse.TempLocation},
+					"chunk_offset":  []string{strconv.FormatInt(chunkOffset, 10)},
+					"chunk_size":    []string{strconv.FormatInt(currentChunkSize, 10)},
+				},
+				MultipartContentName: "file_data", // ..name of the parameter which is the attached file
+				MultipartFileName:    o.remote,    // ..name of the file for the attached file
+
 			}
-			resp, err = o.fs.srv.Call(&opts)
+			resp, err = o.fs.srv.CallJSON(&opts, nil, &reply)
 			return o.fs.shouldRetry(resp, err)
 		})
 		if err != nil {
 			return errors.Wrap(err, "failed to create file")
 		}
-		err = resp.Body.Close()
-		if err != nil {
-			return errors.Wrap(err, "close failed on create file")
+		if reply.TotalWritten != currentChunkSize {
+			return errors.Errorf("failed to create file: incomplete write of %d/%d bytes", reply.TotalWritten, currentChunkSize)
 		}
 
 		chunkCounter++
diff --git a/backend/opendrive/types.go b/backend/opendrive/types.go
index 2cbcf92c1..92aaf29ad 100644
--- a/backend/opendrive/types.go
+++ b/backend/opendrive/types.go
@@ -212,3 +212,7 @@ type permissions struct {
 	FileID       string `json:"file_id"`
 	FileIsPublic int64  `json:"file_ispublic"`
 }
+
+type uploadFileChunkReply struct {
+	TotalWritten int64 `json:"TotalWritten"`
+}