diff --git a/client/withfilesoption.go b/client/withfilesoption.go
index 6edde6e4ae6..eff0d1c25f3 100644
--- a/client/withfilesoption.go
+++ b/client/withfilesoption.go
@@ -91,7 +91,7 @@ func WithFiles() Option {
 			for i, fileData := range filesGroup {
 				mapDataFiles = append(
 					mapDataFiles,
-					fmt.Sprintf(`"%d":[%s]`, i, strings.Join(collect(fileData, wrapMapKeyInQuotes)[:], ",")),
+					fmt.Sprintf(`"%d":[%s]`, i, strings.Join(collect(fileData, wrapMapKeyInQuotes), ",")),
 				)
 			}
 
@@ -105,10 +105,10 @@ func WithFiles() Option {
 		// or
 		// Content-Type: application/octet-stream
 		//
-		for i, fileData := range filesData {
+		for i, fileData := range filesGroup {
 			h := make(textproto.MIMEHeader)
-			h.Set("Content-Disposition", fmt.Sprintf(`form-data; name="%d"; filename="%s"`, i, fileData.file.Name()))
-			b, _ := ioutil.ReadFile(fileData.file.Name())
+			h.Set("Content-Disposition", fmt.Sprintf(`form-data; name="%d"; filename="%s"`, i, fileData[0].file.Name()))
+			b, _ := ioutil.ReadFile(fileData[0].file.Name())
 			h.Set("Content-Type", http.DetectContentType(b))
 			ff, _ := bodyWriter.CreatePart(h)
 			ff.Write(b)
diff --git a/client/withfilesoption_test.go b/client/withfilesoption_test.go
index c404a63629f..02f1a6a8677 100644
--- a/client/withfilesoption_test.go
+++ b/client/withfilesoption_test.go
@@ -209,6 +209,7 @@ func TestWithFiles(t *testing.T) {
 					require.Equal(t, `text/plain; charset=utf-8`, p.Header.Get("Content-Type"))
 					require.Equal(t, []byte(`hello world`), slurp)
 				}
+				require.False(t, regexp.MustCompile(`form-data; name="2"; filename=.*`).MatchString(contentDisposition))
 			}
 			w.Write([]byte(`{}`))
 		})