diff --git a/libbeat/generator/fields/fields.go b/libbeat/generator/fields/fields.go
index b26bf7e36a3..c6210b28d2e 100644
--- a/libbeat/generator/fields/fields.go
+++ b/libbeat/generator/fields/fields.go
@@ -20,6 +20,7 @@ package fields
 import (
 	"bufio"
 	"bytes"
+	"io"
 	"os"
 	"path/filepath"
 	"strings"
@@ -104,28 +105,13 @@ func isLibbeat(beatPath string) bool {
 	return filepath.Base(beatPath) == "libbeat"
 }
 
-func writeGeneratedFieldsYml(fieldFiles []*YmlFile, output string) error {
+func writeGeneratedFieldsYml(fieldFiles []*YmlFile, output io.Writer) error {
 	data, err := GenerateFieldsYml(fieldFiles)
 	if err != nil {
 		return err
 	}
 
-	if output == "-" {
-		fw := bufio.NewWriter(os.Stdout)
-		_, err = fw.Write(data)
-		if err != nil {
-			return err
-		}
-		return fw.Flush()
-	}
-
-	f, err := os.Create(output)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	fw := bufio.NewWriter(f)
+	fw := bufio.NewWriter(output)
 	_, err = fw.Write(data)
 	if err != nil {
 		return err
@@ -164,7 +150,7 @@ func writeIndentedLine(buf *bytes.Buffer, line string, indent int) error {
 }
 
 // Generate collects fields.yml files and concatenates them into one global file.
-func Generate(esBeatsPath, beatPath string, files []*YmlFile, output string) error {
+func Generate(esBeatsPath, beatPath string, files []*YmlFile, output io.Writer) error {
 	files, err := collectCommonFiles(esBeatsPath, beatPath, files)
 	if err != nil {
 		return err
diff --git a/libbeat/scripts/cmd/global_fields/main.go b/libbeat/scripts/cmd/global_fields/main.go
index 41f60e1fe43..b71a848d845 100644
--- a/libbeat/scripts/cmd/global_fields/main.go
+++ b/libbeat/scripts/cmd/global_fields/main.go
@@ -18,8 +18,10 @@
 package main
 
 import (
+	"bytes"
 	"flag"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 
@@ -90,21 +92,29 @@ func main() {
 		fieldsFiles = append(fieldsFiles, fieldsFile...)
 	}
 
-	err = fields.Generate(esBeatsPath, beatPath, fieldsFiles, output)
+	var buffer bytes.Buffer
+	err = fields.Generate(esBeatsPath, beatPath, fieldsFiles, &buffer)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Cannot generate global fields.yml file for %s: %+v\n", name, err)
 		os.Exit(3)
 	}
 
-	_, err = mapping.LoadFieldsYaml(output)
+	_, err = mapping.LoadFields(buffer.Bytes())
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Generated global fields.yml file for %s is invalid: %+v\n", name, err)
 		os.Exit(3)
 	}
 
-	outputPath, _ := filepath.Abs(output)
+	if output == "-" {
+		fmt.Print(buffer.String())
+		return
+	}
+
+	err = ioutil.WriteFile(output, buffer.Bytes(), 0644)
 	if err != nil {
-		outputPath = output
+		fmt.Fprintf(os.Stderr, "Cannot write global fields.yml file for %s: %v", name, err)
 	}
+
+	outputPath, _ := filepath.Abs(output)
 	fmt.Fprintf(os.Stderr, "Generated fields.yml for %s to %s\n", name, outputPath)
 }