diff --git a/misc.go b/misc.go
index a25afb65e..df779c1ad 100644
--- a/misc.go
+++ b/misc.go
@@ -62,13 +62,12 @@ func (e *RateLimitedError) Retryable() bool {
 	return true
 }
 
-func fileUploadReq(ctx context.Context, path string, values url.Values, r io.Reader) (*http.Request, error) {
+func fileUploadReq(ctx context.Context, path string, r io.Reader) (*http.Request, error) {
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, path, r)
 	if err != nil {
 		return nil, err
 	}
 
-	req.URL.RawQuery = values.Encode()
 	return req, nil
 }
 
@@ -155,9 +154,16 @@ func postLocalWithMultipartResponse(ctx context.Context, client httpClient, meth
 func postWithMultipartResponse(ctx context.Context, client httpClient, path, name, fieldname, token string, values url.Values, r io.Reader, intf interface{}, d Debug) error {
 	pipeReader, pipeWriter := io.Pipe()
 	wr := multipart.NewWriter(pipeWriter)
+
 	errc := make(chan error)
 	go func() {
 		defer pipeWriter.Close()
+		defer wr.Close()
+		err := createFormFields(wr, values)
+		if err != nil {
+			errc <- err
+			return
+		}
 		ioWriter, err := wr.CreateFormFile(fieldname, name)
 		if err != nil {
 			errc <- err
@@ -173,7 +179,8 @@ func postWithMultipartResponse(ctx context.Context, client httpClient, path, nam
 			return
 		}
 	}()
-	req, err := fileUploadReq(ctx, path, values, pipeReader)
+
+	req, err := fileUploadReq(ctx, path, pipeReader)
 	if err != nil {
 		return err
 	}
@@ -199,6 +206,20 @@ func postWithMultipartResponse(ctx context.Context, client httpClient, path, nam
 	}
 }
 
+func createFormFields(mw *multipart.Writer, values url.Values) error {
+	for key, value := range values {
+		writer, err := mw.CreateFormField(key)
+		if err != nil {
+			return err
+		}
+		_, err = writer.Write([]byte(value[0]))
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 func doPost(ctx context.Context, client httpClient, req *http.Request, parser responseParser, d Debug) error {
 	resp, err := client.Do(req)
 	if err != nil {
diff --git a/remotefiles.go b/remotefiles.go
index 0467d7e7c..42639a178 100644
--- a/remotefiles.go
+++ b/remotefiles.go
@@ -247,9 +247,7 @@ func (api *Client) UpdateRemoteFile(fileID string, params RemoteFileParameters)
 // Slack API docs: https://api.slack.com/methods/files.remote.update
 func (api *Client) UpdateRemoteFileContext(ctx context.Context, fileID string, params RemoteFileParameters) (remotefile *RemoteFile, err error) {
 	response := &remoteFileResponseFull{}
-	values := url.Values{
-		"token": {api.token},
-	}
+	values := url.Values{}
 	if fileID != "" {
 		values.Add("file", fileID)
 	}
@@ -271,6 +269,7 @@ func (api *Client) UpdateRemoteFileContext(ctx context.Context, fileID string, p
 	if params.PreviewImageReader != nil {
 		err = postWithMultipartResponse(ctx, api.httpclient, api.endpoint+"files.remote.update", "preview.png", "preview_image", api.token, values, params.PreviewImageReader, response, api)
 	} else {
+		values.Add("token", api.token)
 		response, err = api.remoteFileRequest(ctx, "files.remote.update", values)
 	}