diff --git a/Makefile b/Makefile
index a04274d..64570ab 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,7 @@
 .DEFAULT_GOAL := help
 
+SOURCES := $(shell find . -path ./vendor -prune -o -name "*.go" -not -name '*_test.go' -print)
+
 .PHONY: setup
 setup:  ## Setup for required tools.
 	go get -u golang.org/x/lint/golint
@@ -9,8 +11,8 @@ setup:  ## Setup for required tools.
 	dep ensure
 
 .PHONY: fmt
-fmt: ## Formatting source codes.
-	@goimports -w $(find . -type f -name '*.go' -not -path "./vendor/*")
+fmt: $(SOURCES) ## Formatting source codes.
+	@goimports -w $^
 
 .PHONY: lint
 lint: ## Run golint and go vet.
diff --git a/_example/exec-command/main.go b/_example/exec-command/main.go
index 963b81d..838f756 100644
--- a/_example/exec-command/main.go
+++ b/_example/exec-command/main.go
@@ -4,7 +4,7 @@ import (
 	"os"
 	"os/exec"
 
-	"github.com/c-bata/go-prompt"
+	prompt "github.com/c-bata/go-prompt"
 )
 
 func executor(t string) {
diff --git a/_example/http-prompt/main.go b/_example/http-prompt/main.go
index 75d4377..7c16e2d 100644
--- a/_example/http-prompt/main.go
+++ b/_example/http-prompt/main.go
@@ -10,7 +10,7 @@ import (
 	"path"
 	"strings"
 
-	"github.com/c-bata/go-prompt"
+	prompt "github.com/c-bata/go-prompt"
 )
 
 type RequestContext struct {
diff --git a/_example/live-prefix/main.go b/_example/live-prefix/main.go
index ed46295..9c7ced7 100644
--- a/_example/live-prefix/main.go
+++ b/_example/live-prefix/main.go
@@ -3,7 +3,7 @@ package main
 import (
 	"fmt"
 
-	"github.com/c-bata/go-prompt"
+	prompt "github.com/c-bata/go-prompt"
 )
 
 var LivePrefixState struct {
diff --git a/_example/simple-echo/cjk-cyrillic/main.go b/_example/simple-echo/cjk-cyrillic/main.go
index f734e98..3e9e53a 100644
--- a/_example/simple-echo/cjk-cyrillic/main.go
+++ b/_example/simple-echo/cjk-cyrillic/main.go
@@ -3,7 +3,7 @@ package main
 import (
 	"fmt"
 
-	"github.com/c-bata/go-prompt"
+	prompt "github.com/c-bata/go-prompt"
 )
 
 func executor(in string) {
diff --git a/_example/simple-echo/main.go b/_example/simple-echo/main.go
index 01341b1..12b1bb4 100644
--- a/_example/simple-echo/main.go
+++ b/_example/simple-echo/main.go
@@ -3,7 +3,7 @@ package main
 import (
 	"fmt"
 
-	"github.com/c-bata/go-prompt"
+	prompt "github.com/c-bata/go-prompt"
 )
 
 func completer(in prompt.Document) []prompt.Suggest {
diff --git a/_tools/complete_file/main.go b/_tools/complete_file/main.go
index 2c89df1..41015cf 100644
--- a/_tools/complete_file/main.go
+++ b/_tools/complete_file/main.go
@@ -5,7 +5,7 @@ import (
 	"os"
 	"strings"
 
-	"github.com/c-bata/go-prompt"
+	prompt "github.com/c-bata/go-prompt"
 	"github.com/c-bata/go-prompt/completer"
 )
 
diff --git a/_tools/vt100_debug/main.go b/_tools/vt100_debug/main.go
index 8a0dd35..c6cd955 100644
--- a/_tools/vt100_debug/main.go
+++ b/_tools/vt100_debug/main.go
@@ -4,7 +4,7 @@ import (
 	"fmt"
 	"syscall"
 
-	"github.com/c-bata/go-prompt"
+	prompt "github.com/c-bata/go-prompt"
 	"github.com/pkg/term/termios"
 )
 
diff --git a/completer/file.go b/completer/file.go
index 4755b1d..46c60a7 100644
--- a/completer/file.go
+++ b/completer/file.go
@@ -8,7 +8,7 @@ import (
 	"path/filepath"
 	"runtime"
 
-	"github.com/c-bata/go-prompt"
+	prompt "github.com/c-bata/go-prompt"
 )
 
 var (
diff --git a/completion.go b/completion.go
index 6687987..b4cc293 100644
--- a/completion.go
+++ b/completion.go
@@ -4,7 +4,7 @@ import (
 	"log"
 	"strings"
 
-	"github.com/mattn/go-runewidth"
+	runewidth "github.com/mattn/go-runewidth"
 )
 
 const (
diff --git a/document.go b/document.go
index 06b436a..5d2cb8e 100644
--- a/document.go
+++ b/document.go
@@ -5,7 +5,7 @@ import (
 	"strings"
 	"unicode/utf8"
 
-	"github.com/mattn/go-runewidth"
+	runewidth "github.com/mattn/go-runewidth"
 )
 
 // Document has text displayed in terminal and cursor position.
diff --git a/input_windows.go b/input_windows.go
index f52b538..11be65c 100644
--- a/input_windows.go
+++ b/input_windows.go
@@ -9,7 +9,7 @@ import (
 	"unicode/utf8"
 	"unsafe"
 
-	"github.com/mattn/go-tty"
+	tty "github.com/mattn/go-tty"
 )
 
 const maxReadBytes = 1024
diff --git a/output_windows.go b/output_windows.go
index e93bd95..50cf306 100644
--- a/output_windows.go
+++ b/output_windows.go
@@ -5,7 +5,7 @@ package prompt
 import (
 	"io"
 
-	"github.com/mattn/go-colorable"
+	colorable "github.com/mattn/go-colorable"
 )
 
 // WindowsWriter is a ConsoleWriter implementation for Win32 console.
diff --git a/render.go b/render.go
index 2d774aa..2f0c0cc 100644
--- a/render.go
+++ b/render.go
@@ -3,7 +3,7 @@ package prompt
 import (
 	"runtime"
 
-	"github.com/mattn/go-runewidth"
+	runewidth "github.com/mattn/go-runewidth"
 )
 
 // Render to render prompt information from state of Buffer.