diff --git a/command/build/command_test.go b/command/build/command_test.go
index c2f1cfb03..433f0ef46 100644
--- a/command/build/command_test.go
+++ b/command/build/command_test.go
@@ -10,8 +10,8 @@ import (
 func testEnvironment() packer.Environment {
 	config := packer.DefaultEnvironmentConfig()
 	config.Ui = &packer.ReaderWriterUi{
-		new(bytes.Buffer),
-		new(bytes.Buffer),
+		Reader: new(bytes.Buffer),
+		Writer: new(bytes.Buffer),
 	}
 
 	env, err := packer.NewEnvironment(config)
diff --git a/packer/environment.go b/packer/environment.go
index c4586fd44..35a5e5ecc 100644
--- a/packer/environment.go
+++ b/packer/environment.go
@@ -68,7 +68,11 @@ type EnvironmentConfig struct {
 func DefaultEnvironmentConfig() *EnvironmentConfig {
 	config := &EnvironmentConfig{}
 	config.Commands = make([]string, 0)
-	config.Ui = &ReaderWriterUi{os.Stdin, os.Stdout}
+	config.Ui = &ReaderWriterUi{
+		Reader: os.Stdin,
+		Writer: os.Stdout,
+	}
+
 	return config
 }
 
diff --git a/packer/environment_test.go b/packer/environment_test.go
index 16bf11854..be9e7d28f 100644
--- a/packer/environment_test.go
+++ b/packer/environment_test.go
@@ -13,8 +13,8 @@ import (
 func testEnvironment() Environment {
 	config := DefaultEnvironmentConfig()
 	config.Ui = &ReaderWriterUi{
-		new(bytes.Buffer),
-		new(bytes.Buffer),
+		Reader: new(bytes.Buffer),
+		Writer: new(bytes.Buffer),
 	}
 
 	env, err := NewEnvironment(config)
@@ -292,7 +292,10 @@ func TestEnvironmentProvisioner_Error(t *testing.T) {
 func TestEnvironment_SettingUi(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)
 
-	ui := &ReaderWriterUi{new(bytes.Buffer), new(bytes.Buffer)}
+	ui := &ReaderWriterUi{
+		Reader: new(bytes.Buffer),
+		Writer: new(bytes.Buffer),
+	}
 
 	config := &EnvironmentConfig{}
 	config.Ui = ui
diff --git a/packer/rpc/ui.go b/packer/rpc/ui.go
index 02d79d7e0..5e7df0afe 100644
--- a/packer/rpc/ui.go
+++ b/packer/rpc/ui.go
@@ -17,6 +17,15 @@ type UiServer struct {
 	ui packer.Ui
 }
 
+func (u *Ui) Ask(query string) string {
+	var result string
+	if err := u.client.Call("Ui.Ask", query, &result); err != nil {
+		panic(err)
+	}
+
+	return result
+}
+
 func (u *Ui) Error(message string) {
 	if err := u.client.Call("Ui.Error", message, new(interface{})); err != nil {
 		panic(err)
@@ -35,6 +44,11 @@ func (u *Ui) Say(message string) {
 	}
 }
 
+func (u *UiServer) Ask(query string, reply *string) error {
+	*reply = u.ui.Ask(query)
+	return nil
+}
+
 func (u *UiServer) Error(message *string, reply *interface{}) error {
 	u.ui.Error(*message)
 
diff --git a/packer/rpc/ui_test.go b/packer/rpc/ui_test.go
index ce877d8fe..384b959f2 100644
--- a/packer/rpc/ui_test.go
+++ b/packer/rpc/ui_test.go
@@ -7,6 +7,8 @@ import (
 )
 
 type testUi struct {
+	askCalled bool
+	askQuery string
 	errorCalled    bool
 	errorMessage   string
 	messageCalled  bool
@@ -15,6 +17,12 @@ type testUi struct {
 	sayMessage     string
 }
 
+func (u *testUi) Ask(query string) string {
+	u.askCalled = true
+	u.askQuery = query
+	return "foo"
+}
+
 func (u *testUi) Error(message string) {
 	u.errorCalled = true
 	u.errorMessage = message
@@ -50,6 +58,11 @@ func TestUiRPC(t *testing.T) {
 	uiClient := &Ui{client}
 
 	// Basic error and say tests
+	result := uiClient.Ask("query")
+	assert.True(ui.askCalled, "ask should be called")
+	assert.Equal(ui.askQuery, "query", "should be correct")
+	assert.Equal(result, "foo", "should have correct result")
+
 	uiClient.Error("message")
 	assert.Equal(ui.errorMessage, "message", "message should be correct")
 
diff --git a/packer/ui.go b/packer/ui.go
index e32faf8b8..c702b09f5 100644
--- a/packer/ui.go
+++ b/packer/ui.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"sync"
 )
 
 type UiColor uint
@@ -21,6 +22,7 @@ const (
 // world. This sort of control allows us to strictly control how output
 // is formatted and various levels of output.
 type Ui interface {
+	Ask(string) string
 	Say(string)
 	Message(string)
 	Error(string)
@@ -46,6 +48,11 @@ type PrefixedUi struct {
 type ReaderWriterUi struct {
 	Reader io.Reader
 	Writer io.Writer
+	l      sync.Mutex
+}
+
+func (u *ColoredUi) Ask(query string) string {
+	return u.Ui.Ask(u.colorize(query, u.Color, true))
 }
 
 func (u *ColoredUi) Say(message string) {
@@ -74,6 +81,10 @@ func (u *ColoredUi) colorize(message string, color UiColor, bold bool) string {
 	return fmt.Sprintf("\033[%d;%d;40m%s\033[0m", attr, color, message)
 }
 
+func (u *PrefixedUi) Ask(query string) string {
+	return u.Ui.Ask(fmt.Sprintf("%s: %s", u.SayPrefix, query))
+}
+
 func (u *PrefixedUi) Say(message string) {
 	u.Ui.Say(fmt.Sprintf("%s: %s", u.SayPrefix, message))
 }
@@ -86,7 +97,29 @@ func (u *PrefixedUi) Error(message string) {
 	u.Ui.Error(fmt.Sprintf("%s: %s", u.SayPrefix, message))
 }
 
+func (rw *ReaderWriterUi) Ask(query string) string {
+	rw.l.Lock()
+	defer rw.l.Unlock()
+
+	log.Printf("ui: ask: %s", query)
+	if query != "" {
+		if _, err := fmt.Fprint(rw.Writer, query+" "); err != nil {
+			panic(err)
+		}
+	}
+
+	var line string
+	if _, err := fmt.Fscanln(rw.Reader, &line); err != nil {
+		panic(err)
+	}
+
+	return line
+}
+
 func (rw *ReaderWriterUi) Say(message string) {
+	rw.l.Lock()
+	defer rw.l.Unlock()
+
 	log.Printf("ui: %s", message)
 	_, err := fmt.Fprint(rw.Writer, message+"\n")
 	if err != nil {
@@ -95,6 +128,9 @@ func (rw *ReaderWriterUi) Say(message string) {
 }
 
 func (rw *ReaderWriterUi) Message(message string) {
+	rw.l.Lock()
+	defer rw.l.Unlock()
+
 	log.Printf("ui: %s", message)
 	_, err := fmt.Fprintf(rw.Writer, message+"\n")
 	if err != nil {
@@ -103,6 +139,9 @@ func (rw *ReaderWriterUi) Message(message string) {
 }
 
 func (rw *ReaderWriterUi) Error(message string) {
+	rw.l.Lock()
+	defer rw.l.Unlock()
+
 	log.Printf("ui error: %s", message)
 	_, err := fmt.Fprint(rw.Writer, message+"\n")
 	if err != nil {
diff --git a/packer/ui_test.go b/packer/ui_test.go
index 8978f6fc1..bc3191a86 100644
--- a/packer/ui_test.go
+++ b/packer/ui_test.go
@@ -8,8 +8,8 @@ import (
 
 func testUi() *ReaderWriterUi {
 	return &ReaderWriterUi{
-		new(bytes.Buffer),
-		new(bytes.Buffer),
+		Reader: new(bytes.Buffer),
+		Writer: new(bytes.Buffer),
 	}
 }