diff --git a/operation.go b/operation.go
index 8d2622d..e02d0e6 100644
--- a/operation.go
+++ b/operation.go
@@ -1,9 +1,6 @@
 package readline
 
-import (
-	"io"
-	"os"
-)
+import "io"
 
 type Operation struct {
 	cfg     *Config
@@ -203,11 +200,11 @@ func (o *Operation) ioloop() {
 }
 
 func (o *Operation) Stderr() io.Writer {
-	return &wrapWriter{target: os.Stderr, r: o, t: o.t}
+	return &wrapWriter{target: o.cfg.Stderr, r: o, t: o.t}
 }
 
 func (o *Operation) Stdout() io.Writer {
-	return &wrapWriter{target: os.Stdout, r: o, t: o.t}
+	return &wrapWriter{target: o.cfg.Stdout, r: o, t: o.t}
 }
 
 func (o *Operation) String() (string, error) {
diff --git a/readline.go b/readline.go
index 864cfab..76a25d4 100644
--- a/readline.go
+++ b/readline.go
@@ -1,6 +1,9 @@
 package readline
 
-import "io"
+import (
+	"io"
+	"os"
+)
 
 type Instance struct {
 	t *Terminal
@@ -11,6 +14,24 @@ type Config struct {
 	Prompt       string
 	HistoryFile  string
 	AutoComplete AutoCompleter
+	Stdout       io.Writer
+	Stderr       io.Writer
+
+	inited bool
+}
+
+func (c *Config) Init() error {
+	if c.inited {
+		return nil
+	}
+	c.inited = true
+	if c.Stdout == nil {
+		c.Stdout = os.Stdout
+	}
+	if c.Stderr == nil {
+		c.Stderr = os.Stderr
+	}
+	return nil
 }
 
 func NewEx(cfg *Config) (*Instance, error) {
diff --git a/terminal.go b/terminal.go
index 9165221..2dd6bbf 100644
--- a/terminal.go
+++ b/terminal.go
@@ -23,6 +23,9 @@ type Terminal struct {
 }
 
 func NewTerminal(cfg *Config) (*Terminal, error) {
+	if err := cfg.Init(); err != nil {
+		return nil, err
+	}
 	state, err := MakeRaw(syscall.Stdin)
 	if err != nil {
 		return nil, err
@@ -40,15 +43,15 @@ func NewTerminal(cfg *Config) (*Terminal, error) {
 }
 
 func (t *Terminal) Write(b []byte) (int, error) {
-	return os.Stdout.Write(b)
+	return t.cfg.Stdout.Write(b)
 }
 
 func (t *Terminal) Print(s string) {
-	fmt.Fprintf(os.Stdout, "%s", s)
+	fmt.Fprintf(t.cfg.Stdout, "%s", s)
 }
 
 func (t *Terminal) PrintRune(r rune) {
-	fmt.Fprintf(os.Stdout, "%c", r)
+	fmt.Fprintf(t.cfg.Stdout, "%c", r)
 }
 
 func (t *Terminal) Readline() *Operation {